Determine mask UVs based on texture size

cc/trees/layer_tree_host_pixeltest_masks.cc

Index: cc/trees/layer_tree_host_pixeltest_masks.cc
diff --git a/cc/trees/layer_tree_host_pixeltest_masks.cc b/cc/trees/layer_tree_host_pixeltest_masks.cc
index eed99f6a625e026151c71b62a9767b34c683bc5e..c1dac76dedad4ea177b6fb5dccd23ae3c0c77eb6 100644
--- a/cc/trees/layer_tree_host_pixeltest_masks.cc
+++ b/cc/trees/layer_tree_host_pixeltest_masks.cc
@@ -148,6 +148,27 @@ TEST_P(LayerTreeHostMasksPixelTest, MaskOfClippedLayer) {
       base::FilePath(FILE_PATH_LITERAL("mask_of_clipped_layer.png")));
 }
 
+TEST_P(LayerTreeHostMasksPixelTest, MaskOfLargerLayer) {
+  scoped_refptr<SolidColorLayer> background =
+      CreateSolidColorLayer(gfx::Rect(100, 100), SK_ColorWHITE);
+
+  scoped_refptr<SolidColorLayer> green = CreateSolidColorLayerWithBorder(
+      gfx::Rect(0, 0, 100, 100), kCSSGreen, 1, SK_ColorBLACK);
+  background->AddChild(green);
+
+  gfx::Size mask_bounds(40, 40);
+  MaskContentLayerClient client(mask_bounds);
+  scoped_refptr<PictureLayer> mask = PictureLayer::Create(&client);
+  mask->SetBounds(mask_bounds);
+  mask->SetIsDrawable(true);
+  mask->SetLayerMaskType(Layer::LayerMaskType::SINGLE_TEXTURE_MASK);
+  green->SetMaskLayer(mask.get());
+
+  RunPixelResourceTest(
+      background,
+      base::FilePath(FILE_PATH_LITERAL("mask_of_larger_layer.png")));
+}
+
 class CheckerContentLayerClient : public ContentLayerClient {
  public:
   CheckerContentLayerClient(const gfx::Size& bounds,