Do not skip overdraw optimization for non-display-list-2d canvas

Bug: 776826
Cq-Include-Trybots: master.tryserver.chromium.linux:linux_layout_tests_slimming_paint_v2
Change-Id: I4c1d8898a5a983fc0368e792620696f5d90d788b
Reviewed-on: https://chromium-review.googlesource.com/800750
Commit-Queue: Olivia Lai <xlai@chromium.org>
Reviewed-by: Justin Novosad <junov@chromium.org>
Cr-Commit-Position: refs/heads/master@{#520615}

third_party/WebKit/Source/modules/canvas/canvas2d/BaseRenderingContext2D.cpp

@@ -1823,7 +1823,7 @@ void BaseRenderingContext2D::CheckOverdraw(
     CanvasRenderingContext2DState::ImageType image_type,
     DrawType draw_type) {
   PaintCanvas* c = DrawingCanvas();
-  if (!c || !GetImageBuffer()->IsRecording())
+  if (!c)
     return;
 
   SkRect device_rect;

third_party/WebKit/Source/modules/canvas/canvas2d/CanvasRenderingContext2DTest.cpp

@@ -283,19 +283,15 @@ class FakeAcceleratedImageBufferSurface
 
 //============================================================================
 
-class MockImageBufferSurfaceForOverwriteTesting
-    : public UnacceleratedImageBufferSurface {
+class MockImageBufferSurfaceForOverwriteTesting : public Canvas2DLayerBridge {
  public:
   MockImageBufferSurfaceForOverwriteTesting(const IntSize& size,
                                             CanvasColorParams color_params)
-      : UnacceleratedImageBufferSurface(size,
-                                        kInitializeImagePixels,
-                                        color_params) {}
+      : Canvas2DLayerBridge(size,
+                            0,
+                            Canvas2DLayerBridge::kDisableAcceleration,
+                            color_params) {}
   ~MockImageBufferSurfaceForOverwriteTesting() override {}
-  bool IsRecording() const override {
-    return true;
-  }  // otherwise overwrites are not tracked
-
   MOCK_METHOD0(WillOverwriteCanvas, void());
 };
 

third_party/WebKit/Source/platform/graphics/RecordingImageBufferSurface.cpp

@@ -263,7 +263,8 @@ void RecordingImageBufferSurface::WillOverwriteCanvas() {
   previous_frame_.reset();
   previous_frame_has_expensive_op_ = false;
   previous_frame_pixel_count_ = 0;
-  if (did_record_draw_commands_in_current_frame_) {
+
+  if (did_record_draw_commands_in_current_frame_ && !fallback_surface_) {
     // Discard previous draw commands
     current_frame_->finishRecordingAsPicture();
     InitializeCurrentFrame();