Add a new API for testing animated images

LayoutTests/canvas/philip/tests/2d.drawImage.animated.gif.html

Index: LayoutTests/canvas/philip/tests/2d.drawImage.animated.gif.html
diff --git a/LayoutTests/canvas/philip/tests/2d.drawImage.animated.gif.html b/LayoutTests/canvas/philip/tests/2d.drawImage.animated.gif.html
index 44dc495d1b5f25b3992494140b63f833004f887f..7369aff26369de826c57ae0749dfdc6312f80762 100644
--- a/LayoutTests/canvas/philip/tests/2d.drawImage.animated.gif.html
+++ b/LayoutTests/canvas/philip/tests/2d.drawImage.animated.gif.html
@@ -13,11 +13,14 @@
 _addTest(function(canvas, ctx) {
 
 deferTest();
-setTimeout(wrapFunction(function () {
+
+// Advance the animation one frame to ensure we only draw the first frame.
+window.internals.advanceImageAnimation(document.getElementById('anim-gr.gif'));
+
+requestAnimationFrame(wrapFunction(function () {
     ctx.drawImage(document.getElementById('anim-gr.gif'), 0, 0);
     _assertPixelApprox(canvas, 50,25, 0,255,0,255, "50,25", "0,255,0,255", 2);
-}), 500);
-
+}));
 
 });
 </script>