diff -r 000000000000 -r 6474c204b198 gfx/thebes/gfxReusableSharedImageSurfaceWrapper.cpp
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/gfx/thebes/gfxReusableSharedImageSurfaceWrapper.cpp	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,98 @@
+/* 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 "gfxReusableSharedImageSurfaceWrapper.h"
+#include "gfxSharedImageSurface.h"
+#include "mozilla/layers/ISurfaceAllocator.h"
+
+using mozilla::ipc::Shmem;
+using mozilla::layers::ISurfaceAllocator;
+
+gfxReusableSharedImageSurfaceWrapper::gfxReusableSharedImageSurfaceWrapper(ISurfaceAllocator* aAllocator,
+                                                                           gfxSharedImageSurface* aSurface)
+  : mAllocator(aAllocator)
+  , mSurface(aSurface)
+{
+  MOZ_COUNT_CTOR(gfxReusableSharedImageSurfaceWrapper);
+  ReadLock();
+}
+
+gfxReusableSharedImageSurfaceWrapper::~gfxReusableSharedImageSurfaceWrapper()
+{
+  MOZ_COUNT_DTOR(gfxReusableSharedImageSurfaceWrapper);
+  ReadUnlock();
+}
+
+void
+gfxReusableSharedImageSurfaceWrapper::ReadLock()
+{
+  NS_ASSERT_OWNINGTHREAD(gfxReusableSharedImageSurfaceWrapper);
+  mSurface->ReadLock();
+}
+
+void
+gfxReusableSharedImageSurfaceWrapper::ReadUnlock()
+{
+  int32_t readCount = mSurface->ReadUnlock();
+  NS_ABORT_IF_FALSE(readCount >= 0, "Read count should not be negative");
+
+  if (readCount == 0) {
+    mAllocator->DeallocShmem(mSurface->GetShmem());
+  }
+}
+
+gfxReusableSurfaceWrapper*
+gfxReusableSharedImageSurfaceWrapper::GetWritable(gfxImageSurface** aSurface)
+{
+  NS_ASSERT_OWNINGTHREAD(gfxReusableSharedImageSurfaceWrapper);
+
+  int32_t readCount = mSurface->GetReadCount();
+  NS_ABORT_IF_FALSE(readCount > 0, "A ReadLock must be held when calling GetWritable");
+  if (readCount == 1) {
+    *aSurface = mSurface;
+    return this;
+  }
+
+  // Something else is reading the surface, copy it
+  nsRefPtr<gfxSharedImageSurface> copySurface =
+    gfxSharedImageSurface::CreateUnsafe(mAllocator.get(), mSurface->GetSize(), mSurface->Format());
+  copySurface->CopyFrom(mSurface);
+  *aSurface = copySurface;
+
+  // We need to create a new wrapper since this wrapper has an external ReadLock
+  gfxReusableSurfaceWrapper* wrapper = new gfxReusableSharedImageSurfaceWrapper(mAllocator, copySurface);
+
+  // No need to release the ReadLock on the surface, this will happen when
+  // the wrapper is destroyed.
+
+  return wrapper;
+}
+
+const unsigned char*
+gfxReusableSharedImageSurfaceWrapper::GetReadOnlyData() const
+{
+  NS_ABORT_IF_FALSE(mSurface->GetReadCount() > 0, "Should have read lock");
+  return mSurface->Data();
+}
+
+gfxImageFormat
+gfxReusableSharedImageSurfaceWrapper::Format()
+{
+  return mSurface->Format();
+}
+
+Shmem&
+gfxReusableSharedImageSurfaceWrapper::GetShmem()
+{
+  return mSurface->GetShmem();
+}
+
+/* static */ already_AddRefed<gfxReusableSharedImageSurfaceWrapper>
+gfxReusableSharedImageSurfaceWrapper::Open(ISurfaceAllocator* aAllocator, const Shmem& aShmem)
+{
+  nsRefPtr<gfxSharedImageSurface> sharedImage = gfxSharedImageSurface::Open(aShmem);
+  nsRefPtr<gfxReusableSharedImageSurfaceWrapper> wrapper = new gfxReusableSharedImageSurfaceWrapper(aAllocator, sharedImage);
+  wrapper->ReadUnlock();
+  return wrapper.forget();
+}