diff -r 000000000000 -r 6474c204b198 gfx/skia/trunk/src/utils/SkFrontBufferedStream.cpp
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/gfx/skia/trunk/src/utils/SkFrontBufferedStream.cpp	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,197 @@
+/*
+ * Copyright 2013 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#include "SkFrontBufferedStream.h"
+#include "SkStream.h"
+#include "SkTemplates.h"
+
+class FrontBufferedStream : public SkStreamRewindable {
+public:
+    // Called by Create.
+    FrontBufferedStream(SkStream*, size_t bufferSize);
+
+    virtual size_t read(void* buffer, size_t size) SK_OVERRIDE;
+
+    virtual bool isAtEnd() const SK_OVERRIDE;
+
+    virtual bool rewind() SK_OVERRIDE;
+
+    virtual bool hasPosition() const SK_OVERRIDE { return true; }
+
+    virtual size_t getPosition() const SK_OVERRIDE { return fOffset; }
+
+    virtual bool hasLength() const SK_OVERRIDE { return fHasLength; }
+
+    virtual size_t getLength() const SK_OVERRIDE { return fLength; }
+
+    virtual SkStreamRewindable* duplicate() const SK_OVERRIDE { return NULL; }
+
+private:
+    SkAutoTUnref<SkStream>  fStream;
+    const bool              fHasLength;
+    const size_t            fLength;
+    // Current offset into the stream. Always >= 0.
+    size_t                  fOffset;
+    // Amount that has been buffered by calls to read. Will always be less than
+    // fBufferSize.
+    size_t                  fBufferedSoFar;
+    // Total size of the buffer.
+    const size_t            fBufferSize;
+    // FIXME: SkAutoTMalloc throws on failure. Instead, Create should return a
+    // NULL stream.
+    SkAutoTMalloc<char>     fBuffer;
+
+    // Read up to size bytes from already buffered data, and copy to
+    // dst, if non-NULL. Updates fOffset. Assumes that fOffset is less
+    // than fBufferedSoFar.
+    size_t readFromBuffer(char* dst, size_t size);
+
+    // Buffer up to size bytes from the stream, and copy to dst if non-
+    // NULL. Updates fOffset and fBufferedSoFar. Assumes that fOffset is
+    // less than fBufferedSoFar, and size is greater than 0.
+    size_t bufferAndWriteTo(char* dst, size_t size);
+
+    // Read up to size bytes directly from the stream and into dst if non-
+    // NULL. Updates fOffset. Assumes fOffset is at or beyond the buffered
+    // data, and size is greater than 0.
+    size_t readDirectlyFromStream(char* dst, size_t size);
+
+    typedef SkStream INHERITED;
+};
+
+SkStreamRewindable* SkFrontBufferedStream::Create(SkStream* stream, size_t bufferSize) {
+    if (NULL == stream) {
+        return NULL;
+    }
+    return SkNEW_ARGS(FrontBufferedStream, (stream, bufferSize));
+}
+
+FrontBufferedStream::FrontBufferedStream(SkStream* stream, size_t bufferSize)
+    : fStream(SkRef(stream))
+    , fHasLength(stream->hasPosition() && stream->hasLength())
+    , fLength(stream->getLength() - stream->getPosition())
+    , fOffset(0)
+    , fBufferedSoFar(0)
+    , fBufferSize(bufferSize)
+    , fBuffer(bufferSize) {}
+
+bool FrontBufferedStream::isAtEnd() const {
+    if (fOffset < fBufferedSoFar) {
+        // Even if the underlying stream is at the end, this stream has been
+        // rewound after buffering, so it is not at the end.
+        return false;
+    }
+
+    return fStream->isAtEnd();
+}
+
+bool FrontBufferedStream::rewind() {
+    // Only allow a rewind if we have not exceeded the buffer.
+    if (fOffset <= fBufferSize) {
+        fOffset = 0;
+        return true;
+    }
+    return false;
+}
+
+size_t FrontBufferedStream::readFromBuffer(char* dst, size_t size) {
+    SkASSERT(fOffset < fBufferedSoFar);
+    // Some data has already been copied to fBuffer. Read up to the
+    // lesser of the size requested and the remainder of the buffered
+    // data.
+    const size_t bytesToCopy = SkTMin(size, fBufferedSoFar - fOffset);
+    if (dst != NULL) {
+        memcpy(dst, fBuffer + fOffset, bytesToCopy);
+    }
+
+    // Update fOffset to the new position. It is guaranteed to be
+    // within the buffered data.
+    fOffset += bytesToCopy;
+    SkASSERT(fOffset <= fBufferedSoFar);
+
+    return bytesToCopy;
+}
+
+size_t FrontBufferedStream::bufferAndWriteTo(char* dst, size_t size) {
+    SkASSERT(size > 0);
+    SkASSERT(fOffset >= fBufferedSoFar);
+    // Data needs to be buffered. Buffer up to the lesser of the size requested
+    // and the remainder of the max buffer size.
+    const size_t bytesToBuffer = SkTMin(size, fBufferSize - fBufferedSoFar);
+    char* buffer = fBuffer + fOffset;
+    const size_t buffered = fStream->read(buffer, bytesToBuffer);
+
+    fBufferedSoFar += buffered;
+    fOffset = fBufferedSoFar;
+    SkASSERT(fBufferedSoFar <= fBufferSize);
+
+    // Copy the buffer to the destination buffer and update the amount read.
+    if (dst != NULL) {
+        memcpy(dst, buffer, buffered);
+    }
+
+    return buffered;
+}
+
+size_t FrontBufferedStream::readDirectlyFromStream(char* dst, size_t size) {
+    SkASSERT(size > 0);
+    // If we get here, we have buffered all that can be buffered.
+    SkASSERT(fBufferSize == fBufferedSoFar && fOffset >= fBufferSize);
+
+    const size_t bytesReadDirectly = fStream->read(dst, size);
+    fOffset += bytesReadDirectly;
+
+    // If we have read past the end of the buffer, rewinding is no longer
+    // supported, so we can go ahead and free the memory.
+    if (bytesReadDirectly > 0) {
+        fBuffer.reset(0);
+    }
+
+    return bytesReadDirectly;
+}
+
+size_t FrontBufferedStream::read(void* voidDst, size_t size) {
+    // Cast voidDst to a char* for easy addition.
+    char* dst = reinterpret_cast<char*>(voidDst);
+    SkDEBUGCODE(const size_t totalSize = size;)
+    const size_t start = fOffset;
+
+    // First, read any data that was previously buffered.
+    if (fOffset < fBufferedSoFar) {
+        const size_t bytesCopied = this->readFromBuffer(dst, size);
+
+        // Update the remaining number of bytes needed to read
+        // and the destination buffer.
+        size -= bytesCopied;
+        SkASSERT(size + (fOffset - start) == totalSize);
+        if (dst != NULL) {
+            dst += bytesCopied;
+        }
+    }
+
+    // Buffer any more data that should be buffered, and copy it to the
+    // destination.
+    if (size > 0 && fBufferedSoFar < fBufferSize) {
+        const size_t buffered = this->bufferAndWriteTo(dst, size);
+
+        // Update the remaining number of bytes needed to read
+        // and the destination buffer.
+        size -= buffered;
+        SkASSERT(size + (fOffset - start) == totalSize);
+        if (dst != NULL) {
+            dst += buffered;
+        }
+    }
+
+    if (size > 0 && !fStream->isAtEnd()) {
+        SkDEBUGCODE(const size_t bytesReadDirectly =) this->readDirectlyFromStream(dst, size);
+        SkDEBUGCODE(size -= bytesReadDirectly;)
+        SkASSERT(size + (fOffset - start) == totalSize);
+    }
+
+    return fOffset - start;
+}