Make 2D canvas smarter about chosing whether or not to use GPU acceleration

Source/platform/graphics/Canvas2DLayerBridge.h

Index: Source/platform/graphics/Canvas2DLayerBridge.h
diff --git a/Source/platform/graphics/Canvas2DLayerBridge.h b/Source/platform/graphics/Canvas2DLayerBridge.h
index 62bfef350138f3a8e8134671f46950b8c1471358..174366b12a4c9fe504dd79af875dcef43b8215d9 100644
--- a/Source/platform/graphics/Canvas2DLayerBridge.h
+++ b/Source/platform/graphics/Canvas2DLayerBridge.h
@@ -51,7 +51,13 @@ class WebGraphicsContext3DProvider;
 class PLATFORM_EXPORT Canvas2DLayerBridge : public WebExternalTextureLayerClient, public RefCounted<Canvas2DLayerBridge> {
     WTF_MAKE_NONCOPYABLE(Canvas2DLayerBridge);
 public:
-    static PassRefPtr<Canvas2DLayerBridge> create(const IntSize&, OpacityMode, int msaaSampleCount);
+    enum AccelerationMode {
+        DisableAcceleration,
+        EnableAcceleration,
+        ForceAcceleration,

[Stephen White, 2015/09/15 20:43:58]

Please rename ForceAcceleration -> ForceAccelerationForTesting.

+    };
+
+    static PassRefPtr<Canvas2DLayerBridge> create(const IntSize&, int msaaSampleCount, OpacityMode, AccelerationMode);
 
     ~Canvas2DLayerBridge() override;
 
@@ -69,7 +75,7 @@ public:
     bool checkSurfaceValid();
     bool restoreSurface();
     WebLayer* layer() const;
-    bool isAccelerated() const { return true; }
+    bool isAccelerated() const;
     void setFilterQuality(SkFilterQuality);
     void setIsHidden(bool);
     void setImageBuffer(ImageBuffer*);
@@ -77,21 +83,23 @@ public:
     bool writePixels(const SkImageInfo&, const void* pixels, size_t rowBytes, int x, int y);
     void flush();
     void flushGpu();
-
+    void prepareSurfaceForPaintingIfNeeded();
     void limitPendingFrames();
     bool isHidden() { return m_isHidden; }
 
     void beginDestruction();
 
-    PassRefPtr<SkImage> newImageSnapshot();
+    PassRefPtr<SkImage> newImageSnapshot(AccelerationHint);
 
 private:
-    Canvas2DLayerBridge(PassOwnPtr<WebGraphicsContext3DProvider>, PassRefPtr<SkSurface>, int, OpacityMode);
+    Canvas2DLayerBridge(PassOwnPtr<WebGraphicsContext3DProvider>, const IntSize&, int msaaSampleCount, OpacityMode, AccelerationMode);
     void setRateLimitingEnabled(bool);
     WebGraphicsContext3D* context();
     void startRecording();
     void skipQueuedDrawCommands();
     void flushRecordingOnly();
+    SkSurface* surface(AccelerationHint = PreferAcceleration);

[Stephen White, 2015/09/15 20:43:58]

<bikeshed> Prefer a name that indicates that this is not just an accessor.
getOrCreateSurface(), or ensureSurface(), or something. </bikeshed>

+    bool shouldAccelerate(AccelerationHint) const;
 
     OwnPtr<SkPictureRecorder> m_recorder;
     RefPtr<SkSurface> m_surface;
@@ -131,6 +139,7 @@ private:
 
     Deque<MailboxInfo, MaxActiveMailboxes> m_mailboxes;
     GLenum m_lastFilter;
+    AccelerationMode m_accelerationMode;
     OpacityMode m_opacityMode;
     IntSize m_size;
     int m_recordingPixelCount;