Use std::unique_ptr to signal ownership transfer in WebCompositorSupport

third_party/WebKit/public/platform/WebCompositorSupport.h

Index: third_party/WebKit/public/platform/WebCompositorSupport.h
diff --git a/third_party/WebKit/public/platform/WebCompositorSupport.h b/third_party/WebKit/public/platform/WebCompositorSupport.h
index 6a90e22d14964c90c005201671471c5d7b1e11d9..0ef1b3cae2ef242aabb671c3339e263b01e70d45 100644
--- a/third_party/WebKit/public/platform/WebCompositorSupport.h
+++ b/third_party/WebKit/public/platform/WebCompositorSupport.h
@@ -32,6 +32,8 @@
 #include "WebScrollbar.h"
 #include "WebScrollbarThemePainter.h"
 
+#include <memory>
+
 namespace cc {
 class Layer;
 class TextureLayerClient;
@@ -51,36 +53,28 @@ class WebCompositorSupport {
  public:
   // Layers -------------------------------------------------------
 
-  virtual WebLayer* createLayer() { return nullptr; }
+  virtual std::unique_ptr<WebLayer> createLayer() = 0;
 
-  virtual WebLayer* createLayerFromCCLayer(cc::Layer*) { return nullptr; }
+  virtual std::unique_ptr<WebLayer> createLayerFromCCLayer(cc::Layer*) = 0;
 
-  virtual WebContentLayer* createContentLayer(WebContentLayerClient*) {
-    return nullptr;
-  }
+  virtual std::unique_ptr<WebContentLayer> createContentLayer(
+      WebContentLayerClient*) = 0;
 
-  virtual WebExternalTextureLayer* createExternalTextureLayer(
-      cc::TextureLayerClient*) {
-    return nullptr;
-  }
+  virtual std::unique_ptr<WebExternalTextureLayer> createExternalTextureLayer(
+      cc::TextureLayerClient*) = 0;
 
-  virtual WebImageLayer* createImageLayer() { return nullptr; }
+  virtual std::unique_ptr<WebImageLayer> createImageLayer() = 0;
 
-  // The ownership of the WebScrollbarThemeGeometry pointer is passed to
-  // Chromium.
-  virtual WebScrollbarLayer* createScrollbarLayer(WebScrollbar*,
-                                                  WebScrollbarThemePainter,
-                                                  WebScrollbarThemeGeometry*) {
-    return nullptr;
-  }
+  virtual std::unique_ptr<WebScrollbarLayer> createScrollbarLayer(
+      std::unique_ptr<WebScrollbar>,
+      WebScrollbarThemePainter,
+      std::unique_ptr<WebScrollbarThemeGeometry>) = 0;
 
-  virtual WebScrollbarLayer* createSolidColorScrollbarLayer(
+  virtual std::unique_ptr<WebScrollbarLayer> createSolidColorScrollbarLayer(
       WebScrollbar::Orientation,
       int thumbThickness,
       int trackStart,
-      bool isLeftSideVerticalScrollbar) {
-    return nullptr;
-  }
+      bool isLeftSideVerticalScrollbar) = 0;
 
  protected:
   virtual ~WebCompositorSupport() {}