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");
+
+var recoveryLoopPeriod = 5;
+var ctx;
+var imageData;
+var imgdata;
+
+if (window.internals && window.testRunner) {
+    testRunner.dumpAsText();
+    ctx = document.createElement('canvas').getContext('2d');
+    document.body.appendChild(ctx.canvas);
+    ctx.fillStyle = '#f00';
+    ctx.fillRect(0, 0, ctx.canvas.width, ctx.canvas.height);
+    imageData = ctx.getImageData(0, 0, 1, 1);
+    imgdata = imageData.data;
+    shouldBe("imgdata[0]", "255");
+    shouldBe("imgdata[1]", "0");
+    shouldBe("imgdata[2]", "0");
+    shouldBe("imgdata[3]", "255");
+
+    window.internals.loseSharedGraphicsContext3D();
+    // Verify whether canvas contents are lost with the graphics context.
+    imageData = ctx.getImageData(0, 0, 1, 1);
+    if (imageData.data[0] == 255) {
+        debug('<span>Aborting test: Graphics context loss did not destroy canvas contents. This is expected if canvas is not accelerated.</span>');
+    } else {
+        // Redrawing immediately will fail because we are working with an
+        // unrecovered context here. The context recovery is asynchronous
+        // because it requires the context loss notification task to be
+        // processed on the renderer main thread, which triggers the
+        // re-creation of the SharedGC3D.
+        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]", "0");
+        shouldBe("imgdata[2]", "0");
+        shouldBe("imgdata[3]", "0");
+
+        testRunner.waitUntilDone();
+        setTimeout(recoveryLoop, recoveryLoopPeriod);
+    }
+} else {
+    testFailed('This test requires window.internals and window.testRunner.');
+}
+
+// Graphics context recovery happens asynchronously.  To test for recovery, we keep
+// retrying to use the canvas until it succeeds, which should hapen long before the test
+// times-out.
+function recoveryLoop() {
+    ctx.fillStyle = '#00f';
+    ctx.fillRect(0, 0, ctx.canvas.width, ctx.canvas.height);
+    imageData = ctx.getImageData(0, 0, 1, 1);
+    if (imageData.data[2] == 255) {
+        testPassed('Graphics context recovered.');
+        testRunner.notifyDone();
+    } else {
+        // Context not yet recovered.  Try again.
+        setTimeout(recoveryLoop, recoveryLoopPeriod);
+    }
+}