Fix display list canvas fallback to GPU accelerated mode

Right now when the display list canvas fallback is triggered,
and the fallback canvas is GPU-acclerated, we fail to notify
the GraphicsContext that it has become
accelerated.  This causes HTMLCanvasElement::paint to use
the CPU rendering code path. This change fix the problem by
notifying the GraphicsContext of whether GPU acceleration
is use by the fallback canvas.

BUG=426169

Review URL: https://codereview.chromium.org/669993004

git-svn-id: svn://svn.chromium.org/blink/trunk@184379 bbb929c8-8fbe-4397-9dbb-9b2b20218538

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

@@ -103,6 +103,7 @@ void RecordingImageBufferSurface::fallBackToRasterCanvas()
     if (m_imageBuffer) {
         m_imageBuffer->context()->setRegionTrackingMode(GraphicsContext::RegionTrackingDisabled);
         m_imageBuffer->context()->resetCanvas(m_fallbackSurface->canvas());
+        m_imageBuffer->context()->setAccelerated(m_fallbackSurface->isAccelerated());
     }
 }