Fix canvas blink_perf tests to avoid GPU fallback

third_party/WebKit/PerformanceTests/Canvas/draw-dynamic-webgl-to-hw-accelerated-canvas-2d.html

Index: third_party/WebKit/PerformanceTests/Canvas/draw-dynamic-webgl-to-hw-accelerated-canvas-2d.html
diff --git a/third_party/WebKit/PerformanceTests/Canvas/draw-dynamic-webgl-to-hw-accelerated-canvas-2d.html b/third_party/WebKit/PerformanceTests/Canvas/draw-dynamic-webgl-to-hw-accelerated-canvas-2d.html
index 11fc67dd07e13f61fd1d9f1d8f564f14d1bfbe0d..c35f28ca4b8210cfe55cc8e0a530855f72c6833b 100644
--- a/third_party/WebKit/PerformanceTests/Canvas/draw-dynamic-webgl-to-hw-accelerated-canvas-2d.html
+++ b/third_party/WebKit/PerformanceTests/Canvas/draw-dynamic-webgl-to-hw-accelerated-canvas-2d.html
@@ -11,6 +11,12 @@ var gl = canvas3D.getContext('webgl');
 if (!gl)
     CanvasRunner.logFatalError("WebGL is not supported or enabled on this platform!");
 
+var dummyCanvas2D = document.createElement("canvas");
+var dummyCtx2D = dummyCanvas2D.getContext("2d");
+
+dummyCanvas2D.width = 1;
+dummyCanvas2D.height = 1;
+
 function setSize(canvas2DWidth, canvas2DHeight, webglWidth, webglHeight) {
     canvas2D.width = canvas2DWidth;
     canvas2D.height = canvas2DHeight;
@@ -38,9 +44,9 @@ function doRun() {
 }
 
 function ensureComplete() {
-    // Calling getImageData() is just to flush out the content when
-    // accelerated 2D canvas is in use. The cost of reading 1x1 pixels is low.
-    ctx2D.getImageData(0, 0, 1, 1);
+    // Using destCanvas2D as a source image is just to flush out the content when
+    // accelerated 2D canvas is in use. 
+    dummyCtx2D.drawImage(destCanvas2D, 0, 0, 1, 1, 0, 0, 1, 1);
 }
 
 window.onload = function () {