2D Canvas: Refactor code re-attempting to allocate an imageBuffer.

LayoutTests/fast/canvas/script-tests/canvas-extremely-large-dimensions.js

+description("Series of tests to ensure correct behaviour when canvas size is extremely large.");
+var canvas = document.createElement('canvas')
+var ctx = canvas.getContext('2d');
+
+// WebIDL defines width and height as int. 2147483647 is int max.
+var extremelyLargeNumber = 2147483647;
+canvas.width = extremelyLargeNumber;
+canvas.height = extremelyLargeNumber;
+
+debug("check for crash on extremely large canvas size.");
+useCanvasContext(ctx);
+var imageData = ctx.getImageData(1, 1, 98, 98);
+var imgdata = imageData.data;
+// Blink returns zero color if the image buffer does not exist.
+shouldBe("imgdata[4]", "0");
+shouldBe("imgdata[5]", "0");
+shouldBe("imgdata[6]", "0");
+
+debug("check for crash after resetting to the same size.");
+canvas.width = extremelyLargeNumber;
+useCanvasContext(ctx);
+imageData = ctx.getImageData(1, 1, 98, 98);
+imgdata = imageData.data;
+shouldBe("imgdata[4]", "0");
+shouldBe("imgdata[5]", "0");
+shouldBe("imgdata[6]", "0");
+
+// googol is parsed to 0.
+var googol = Math.pow(10, 100);
+debug("check for crash after resizing to googol.");
+canvas.width = googol;
+canvas.height = googol;
+useCanvasContext(ctx);
+imageData = ctx.getImageData(1, 1, 98, 98);
+imgdata = imageData.data;
+shouldBe("imgdata[4]", "0");
+shouldBe("imgdata[5]", "0");
+shouldBe("imgdata[6]", "0");
+
+debug("check for crash after resetting to the same size.");
+canvas.width = googol;
+useCanvasContext(ctx);
+imageData = ctx.getImageData(1, 1, 98, 98);
+imgdata = imageData.data;
+shouldBe("imgdata[4]", "0");
+shouldBe("imgdata[5]", "0");
+shouldBe("imgdata[6]", "0");
+
+debug("check again for crash on extremely large canvas size.");
+canvas.width = extremelyLargeNumber;
+canvas.height = extremelyLargeNumber;
+useCanvasContext(ctx);
+imageData = ctx.getImageData(1, 1, 98, 98);
+imgdata = imageData.data;
+shouldBe("imgdata[4]", "0");
+shouldBe("imgdata[5]", "0");
+shouldBe("imgdata[6]", "0");
+
+function useCanvasContext(ctx) {
+    ctx.fillStyle = 'green';
+    ctx.fillRect(0, 0, 100, 100);
+    for(var i = 0; i < 100; i++) {
+        // This API tries to create an image buffer if the image buffer is not created.
+        ctx.getImageData(1, 1, 1, 1);
+    }
+    ctx.beginPath();
+    ctx.rect(0,0,100,100);
+    ctx.save();
+    ctx.fillStyle = 'red';
+    ctx.fillRect(0, 0, 100, 100);
+    ctx.restore();
+    ctx.fillStyle = 'green';
+    ctx.fill();
+}
+
+debug("after resizing to normal size, the canvas must be in a valid state.");
+canvas.width = 100;
+canvas.height = 100;
+ctx.fillStyle = 'blue';
+ctx.fillRect(0, 0, 100, 100);
+imageData = ctx.getImageData(1, 1, 98, 98);
+imgdata = imageData.data;
+shouldBe("imgdata[4]", "0");
+shouldBe("imgdata[5]", "0");
+shouldBe("imgdata[6]", "255");