diff -r 000000000000 -r 6474c204b198 gfx/thebes/gfxSkipChars.cpp
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/gfx/thebes/gfxSkipChars.cpp	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,140 @@
+/* -*- Mode: C++; tab-width: 20; indent-tabs-mode: nil; c-basic-offset: 4 -*-
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "gfxSkipChars.h"
+
+void
+gfxSkipCharsIterator::SetOriginalOffset(int32_t aOffset)
+{
+    aOffset += mOriginalStringToSkipCharsOffset;
+    NS_ASSERTION(uint32_t(aOffset) <= mSkipChars->mCharCount,
+                 "Invalid offset");
+
+    mOriginalStringOffset = aOffset;
+
+    uint32_t rangeCount = mSkipChars->mRanges.Length();
+    if (rangeCount == 0) {
+        mSkippedStringOffset = aOffset;
+        return;
+    }
+
+    // at start of string?
+    if (aOffset == 0) {
+        mSkippedStringOffset = 0;
+        mCurrentRangeIndex =
+            rangeCount && mSkipChars->mRanges[0].Start() == 0 ? 0 : -1;
+        return;
+    }
+
+    // find the range that includes or precedes aOffset
+    uint32_t lo = 0, hi = rangeCount;
+    const gfxSkipChars::SkippedRange* ranges = mSkipChars->mRanges.Elements();
+    while (lo < hi) {
+        uint32_t mid = (lo + hi) / 2;
+        if (uint32_t(aOffset) < ranges[mid].Start()) {
+            hi = mid;
+        } else {
+            lo = mid + 1;
+        }
+    }
+
+    if (lo == rangeCount) {
+        mCurrentRangeIndex = rangeCount - 1;
+    } else if (uint32_t(aOffset) < ranges[lo].Start()) {
+        mCurrentRangeIndex = lo - 1;
+        if (mCurrentRangeIndex == -1) {
+            mSkippedStringOffset = aOffset;
+            return;
+        }
+    } else {
+        mCurrentRangeIndex = lo;
+    }
+
+    const gfxSkipChars::SkippedRange& r = ranges[mCurrentRangeIndex];
+    if (uint32_t(aOffset) < r.End()) {
+        mSkippedStringOffset = r.SkippedOffset();
+        return;
+    }
+
+    mSkippedStringOffset = aOffset - r.NextDelta();
+}
+
+void
+gfxSkipCharsIterator::SetSkippedOffset(uint32_t aOffset)
+{
+    NS_ASSERTION((mSkipChars->mRanges.IsEmpty() &&
+                  aOffset <= mSkipChars->mCharCount) ||
+                 (aOffset <= mSkipChars->LastRange().SkippedOffset() +
+                                 mSkipChars->mCharCount -
+                                 mSkipChars->LastRange().End()),
+                 "Invalid skipped offset");
+    mSkippedStringOffset = aOffset;
+
+    uint32_t rangeCount = mSkipChars->mRanges.Length();
+    if (rangeCount == 0) {
+        mOriginalStringOffset = aOffset;
+        return;
+    }
+
+    uint32_t lo = 0, hi = rangeCount;
+    const gfxSkipChars::SkippedRange* ranges = mSkipChars->mRanges.Elements();
+    while (lo < hi) {
+        uint32_t mid = (lo + hi) / 2;
+        if (aOffset < ranges[mid].SkippedOffset()) {
+            hi = mid;
+        } else {
+            lo = mid + 1;
+        }
+    }
+
+    if (lo == rangeCount) {
+        mCurrentRangeIndex = rangeCount - 1;
+    } else if (aOffset < ranges[lo].SkippedOffset()) {
+        mCurrentRangeIndex = lo - 1;
+        if (mCurrentRangeIndex == -1) {
+            mOriginalStringOffset = aOffset;
+            return;
+        }
+    } else {
+        mCurrentRangeIndex = lo;
+    }
+
+    const gfxSkipChars::SkippedRange& r = ranges[mCurrentRangeIndex];
+    mOriginalStringOffset = r.End() + aOffset - r.SkippedOffset();
+}
+
+bool
+gfxSkipCharsIterator::IsOriginalCharSkipped(int32_t* aRunLength) const
+{
+    if (mCurrentRangeIndex == -1) {
+        // we're before the first skipped range (if any)
+        if (aRunLength) {
+            uint32_t end = mSkipChars->mRanges.IsEmpty() ?
+                mSkipChars->mCharCount : mSkipChars->mRanges[0].Start();
+            *aRunLength = end - mOriginalStringOffset;
+        }
+        return mSkipChars->mCharCount == uint32_t(mOriginalStringOffset);
+    }
+
+    const gfxSkipChars::SkippedRange& range =
+        mSkipChars->mRanges[mCurrentRangeIndex];
+
+    if (uint32_t(mOriginalStringOffset) < range.End()) {
+        if (aRunLength) {
+            *aRunLength = range.End() - mOriginalStringOffset;
+        }
+        return true;
+    }
+
+    if (aRunLength) {
+        uint32_t end =
+            uint32_t(mCurrentRangeIndex) + 1 < mSkipChars->mRanges.Length() ?
+                mSkipChars->mRanges[mCurrentRangeIndex + 1].Start() :
+                mSkipChars->mCharCount;
+        *aRunLength = end - mOriginalStringOffset;
+    }
+
+    return mSkipChars->mCharCount == uint32_t(mOriginalStringOffset);
+}