Determine mask UVs based on texture size

cc/trees/layer_tree_host_pixeltest_masks.cc

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include <stddef.h>
 
 #include "build/build_config.h"
 #include "cc/layers/content_layer_client.h"
 #include "cc/layers/picture_image_layer.h"
 #include "cc/layers/picture_layer.h"
@@ skipping 130 matching lines @@
   mask->SetBounds(mask_bounds);
   mask->SetIsDrawable(true);
   mask->SetLayerMaskType(Layer::LayerMaskType::MULTI_TEXTURE_MASK);
   green->SetMaskLayer(mask.get());
 
   RunPixelResourceTest(
       background,
       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,
                            SkColor color,
                            bool vertical)
       : bounds_(bounds), color_(color), vertical_(vertical) {}
   ~CheckerContentLayerClient() override {}
   bool FillsBoundsCompletely() const override { return false; }
   size_t GetApproximateUnsharedMemoryUsage() const override { return 0; }
   gfx::Rect PaintableRegion() override { return gfx::Rect(bounds_); }
@@ skipping 173 matching lines @@
 
   RunPixelResourceTest(background,
                        base::FilePath(
                            FILE_PATH_LITERAL("mask_of_layer_with_blend.png")));
 }
 
 }  // namespace
 }  // namespace cc
 
 #endif  // !defined(OS_ANDROID)