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

Source/modules/canvas2d/CanvasRenderingContext2D.cpp

Index: Source/modules/canvas2d/CanvasRenderingContext2D.cpp
diff --git a/Source/modules/canvas2d/CanvasRenderingContext2D.cpp b/Source/modules/canvas2d/CanvasRenderingContext2D.cpp
index 9ef93f60d2cecfd23f54e35b9125f1dd76786506..407e536624bb9c7a08b68c9594e8ed8510a2a5aa 100644
--- a/Source/modules/canvas2d/CanvasRenderingContext2D.cpp
+++ b/Source/modules/canvas2d/CanvasRenderingContext2D.cpp
@@ -1377,7 +1377,8 @@ void CanvasRenderingContext2D::drawImage(CanvasImageSource* imageSource,
     RefPtr<Image> image;
     SourceImageStatus sourceImageStatus = InvalidSourceImageStatus;
     if (!imageSource->isVideoElement()) {
-        image = imageSource->getSourceImageForCanvas(&sourceImageStatus);
+        AccelerationHint hint = canvas()->buffer()->isAccelerated() ? PreferAcceleration : PreferNoAcceleration;
+        image = imageSource->getSourceImageForCanvas(&sourceImageStatus, hint);
         if (sourceImageStatus == UndecodableSourceImageStatus)
             exceptionState.throwDOMException(InvalidStateError, "The HTMLImageElement provided is in the 'broken' state.");
         if (!image || !image->width() || !image->height())
@@ -1485,7 +1486,7 @@ CanvasPattern* CanvasRenderingContext2D::createPattern(const CanvasImageSourceUn
 
     SourceImageStatus status;
     CanvasImageSource* imageSourceInternal = toImageSourceInternal(imageSource);
-    RefPtr<Image> imageForRendering = imageSourceInternal->getSourceImageForCanvas(&status);
+    RefPtr<Image> imageForRendering = imageSourceInternal->getSourceImageForCanvas(&status, PreferNoAcceleration);
 
     switch (status) {
     case NormalSourceImageStatus:
@@ -1775,6 +1776,10 @@ void CanvasRenderingContext2D::schedulePruneLocalFontCacheIfNeeded()
 
 void CanvasRenderingContext2D::didProcessTask()
 {
+    // The rendering surface needs to be prepared now because it will be too late
+    // to create a layer once we are in the paint invalidation phase.
+    canvas()->prepareSurfaceForPaintingIfNeeded();
+
     pruneLocalFontCache(canvas()->document().canvasFontCache()->maxFonts());
     m_pruneLocalFontCacheScheduled = false;
     Platform::current()->currentThread()->removeTaskObserver(this);