diff -r 000000000000 -r 6474c204b198 gfx/thebes/gfxCachedTempSurface.cpp
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/gfx/thebes/gfxCachedTempSurface.cpp	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,106 @@
+/* -*- Mode: C++; tab-width: 20; indent-tabs-mode: nil; c-basic-offset: 2 -*-
+ * 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 "gfxCachedTempSurface.h"
+#include "gfxContext.h"
+#include "mozilla/Attributes.h"
+
+class CachedSurfaceExpirationTracker MOZ_FINAL :
+  public nsExpirationTracker<gfxCachedTempSurface,2> {
+
+public:
+  // With K = 2, this means that surfaces will be released when they are not
+  // used for 1-2 seconds.
+  enum { TIMEOUT_MS = 1000 };
+  CachedSurfaceExpirationTracker()
+    : nsExpirationTracker<gfxCachedTempSurface,2>(TIMEOUT_MS) {}
+
+  ~CachedSurfaceExpirationTracker() {
+    AgeAllGenerations();
+  }
+
+  virtual void NotifyExpired(gfxCachedTempSurface* aSurface) {
+    RemoveObject(aSurface);
+    aSurface->Expire();
+  }
+
+  static void MarkSurfaceUsed(gfxCachedTempSurface* aSurface)
+  {
+    if (aSurface->GetExpirationState()->IsTracked()) {
+      sExpirationTracker->MarkUsed(aSurface);
+      return;
+    }
+
+    if (!sExpirationTracker) {
+      sExpirationTracker = new CachedSurfaceExpirationTracker();
+    }
+    sExpirationTracker->AddObject(aSurface);
+  }
+
+  static void RemoveSurface(gfxCachedTempSurface* aSurface)
+  {
+    if (!sExpirationTracker)
+      return;
+
+    if (aSurface->GetExpirationState()->IsTracked()) {
+      sExpirationTracker->RemoveObject(aSurface);
+    }
+    if (sExpirationTracker->IsEmpty()) {
+      delete sExpirationTracker;
+      sExpirationTracker = nullptr;
+    }
+  }
+
+private:
+  static CachedSurfaceExpirationTracker* sExpirationTracker;
+};
+
+CachedSurfaceExpirationTracker*
+CachedSurfaceExpirationTracker::sExpirationTracker = nullptr;
+
+gfxCachedTempSurface::~gfxCachedTempSurface()
+{
+  CachedSurfaceExpirationTracker::RemoveSurface(this);
+}
+
+already_AddRefed<gfxContext>
+gfxCachedTempSurface::Get(gfxContentType aContentType,
+                          const gfxRect& aRect,
+                          gfxASurface* aSimilarTo)
+{
+  if (mSurface) {
+    /* Verify the current buffer is valid for this purpose */
+    if (mSize.width < aRect.width || mSize.height < aRect.height
+        || mSurface->GetContentType() != aContentType
+        || mType != aSimilarTo->GetType()) {
+      mSurface = nullptr;
+    }
+  }
+
+  bool cleared = false;
+  if (!mSurface) {
+    mSize = gfxIntSize(int32_t(ceil(aRect.width)), int32_t(ceil(aRect.height)));
+    mSurface = aSimilarTo->CreateSimilarSurface(aContentType, mSize);
+    if (!mSurface)
+      return nullptr;
+
+    cleared = true;
+    mType = aSimilarTo->GetType();
+  }
+  mSurface->SetDeviceOffset(-aRect.TopLeft());
+
+  nsRefPtr<gfxContext> ctx = new gfxContext(mSurface);
+  ctx->Rectangle(aRect);
+  ctx->Clip();
+  if (!cleared && aContentType != gfxContentType::COLOR) {
+    ctx->SetOperator(gfxContext::OPERATOR_CLEAR);
+    ctx->Paint();
+    ctx->SetOperator(gfxContext::OPERATOR_OVER);
+  }
+
+  CachedSurfaceExpirationTracker::MarkSurfaceUsed(this);
+
+  return ctx.forget();
+}