[tracing] Implement composable memory usage estimators.

cc/resources/scoped_ui_resource.h

Index: cc/resources/scoped_ui_resource.h
diff --git a/cc/resources/scoped_ui_resource.h b/cc/resources/scoped_ui_resource.h
index 7f3ea4b385c432c8ed90414abe08e2bec17ae0e7..24dfaaf4e424861e96bde3bce481b1eb35acad41 100644
--- a/cc/resources/scoped_ui_resource.h
+++ b/cc/resources/scoped_ui_resource.h
@@ -33,8 +33,8 @@ class CC_EXPORT ScopedUIResource : public UIResourceClient {
   UIResourceId id() { return id_; }
 
   // Returns the memory usage of the bitmap.
-  size_t GetAllocatedSizeInBytes() const {
-    return bitmap_.GetAllocatedSizeInBytes();
+  size_t EstimateMemoryUsage() const {
+    return bitmap_.EstimateMemoryUsage();
   }
 
  protected: