Make CanvasPixelArray pretent to be Uint8ClampedArray

client/tests/client/dom/CanvasPixelArrayTypeAliasTest.dart

Index: client/tests/client/dom/CanvasPixelArrayTypeAliasTest.dart
diff --git a/client/tests/client/dom/CanvasPixelArrayTypeAliasTest.dart b/client/tests/client/dom/CanvasPixelArrayTypeAliasTest.dart
new file mode 100644
index 0000000000000000000000000000000000000000..5aeffb46d01b98854bb1d864f7579eecfa5f3e91
--- /dev/null
+++ b/client/tests/client/dom/CanvasPixelArrayTypeAliasTest.dart
@@ -0,0 +1,51 @@
+#library('CanvasTest');
+#import('../../../../lib/unittest/unittest.dart');
+#import('../../../../lib/unittest/dom_config.dart');
+#import('dart:dom');
+
+// We have aliased the legacy type CanvasPixelArray with the new type
+// Uint8ClampedArray by mapping the CanvasPixelArray type tag to
+// Uint8ClampedArray.  It is not a perfect match since CanvasPixelArray is
+// missing the ArrayBufferView members.  These should appear to be null.
+
+Object confuseType(x) => [1, x, [x], 's'] [1];  // returns 'x'
+
+main() {
+  HTMLCanvasElement canvas;
+  CanvasRenderingContext2D context;
+  int width = 100;
+  int height = 100;
+
+  canvas = document.createElement('canvas');
+  canvas.setAttribute('width', '$width');
+  canvas.setAttribute('height', '$height');
+  document.body.appendChild(canvas);
+
+  context = canvas.getContext('2d');
+
+  useDomConfiguration();
+
+  test('CreateImageData', () {
+    ImageData image = context.createImageData(canvas.width,
+                                              canvas.height);
+    Uint8ClampedArray data = image.data;
+    // It is legal for the dart2js compiler to believe the type of the native
+    // ImageData.data and elides the check, so check the type explicitly:
+    Expect.isTrue(confuseType(data) is Uint8ClampedArray);
+
+    Expect.equals(40000, data.length);
+    checkPixel(data, 0, [0, 0, 0, 0]);
+    checkPixel(data, width * height - 1, [0, 0, 0, 0]);
+
+    data[100] = 200;
+    Expect.equals(200, data[100]);
+  });
+}
+
+void checkPixel(Uint8ClampedArray data, int offset, List<int> rgba)
+{
+  offset *= 4;
+  for (var i = 0; i < 4; ++i) {
+    Expect.equals(rgba[i], data[offset + i]);
+  }
+}