Fixing Canvas2DLayerBridge to handle lost graphics contexts

LayoutTests/fast/canvas/script-tests/canvas-lost-gpu-context.js

+description("Test the behavior of canvas recovery after a gpu context loss");
+
+if (window.internals && window.testRunner) {
+    window.testRunner.dumpAsText();
+    var ctx = document.createElement('canvas').getContext('2d');
+    document.body.appendChild(ctx.canvas);
+    ctx.fillStyle = '#f00';
+    ctx.fillRect(0, 0, ctx.canvas.width, ctx.canvas.height);
+    // context loss is a no-op when not gpu-acelerated, which is fine for this test
+    window.internals.loseSharedGraphicsContext3D();

[Stephen White, 2013/06/18 18:06:57]

I wonder if we should do this four times, to test the three-strikes software
fallback? Not sure, though.

+    //Verify that buffer automatically recovers to a usable state
+    ctx.fillStyle = '#0f0';
+    ctx.fillRect(0, 0, ctx.canvas.width, ctx.canvas.height);
+    imageData = ctx.getImageData(0, 0, 1, 1);
+    imgdata = imageData.data;
+    shouldBe("imgdata[0]", "0");
+    shouldBe("imgdata[1]", "255");
+    shouldBe("imgdata[2]", "0");
+    shouldBe("imgdata[3]", "255");
+} else {
+    testFailed('This test requires window.internals and window.testRunner.');
+}