Implement ImageData constructors.

LayoutTests/fast/canvas/script-tests/canvas-ImageData.js

+description("Test canvas ImageData constructor");
+
+imageData = new ImageData(100, 50);
+
+shouldBeNonNull("imageData");
+shouldBeNonNull("imageData.data");
+shouldBe("imageData.data[11]", "0");
+for (i = 0; i < imageData.data.length; ++i) {
+    imageData.data[i] = 231;
+}
+
+shouldBe("imageData.width", "100");
+shouldBe("imageData.height", "50");
+shouldBe("imageData.data[32]", "231");
+
+shouldThrow("new ImageData(10)");
+shouldThrow("new ImageData(0, 10)");
+shouldThrow("new ImageData(10, 0)");
+shouldThrow("new ImageData('width', 'height')");
+shouldThrow("new ImageData(1 << 31, 1 << 31)");
+
+shouldThrow("new ImageData(new Uint8ClampedArray(0))");
+shouldThrow("new ImageData(new Uint8Array(100), 25)");
+shouldThrow("new ImageData(imageData.data, 0)");
+shouldThrow("new ImageData(imageData.data, 13)");
+shouldThrow("new ImageData(imageData.data, 1 << 31)");
+shouldThrow("new ImageData(imageData.data, 'biggish')");
+shouldThrow("new ImageData(imageData.data, 1 << 24, 1 << 31)");
+
+imageDataFromData = new ImageData(imageData.data, 100);
+shouldBe("imageDataFromData.width", "100");
+shouldBe("imageDataFromData.height", "50");
+shouldBe("imageDataFromData.data[34]", "imageData.data[34]");