More cleanups on the CanvasRenderingContextHost front

- move more things to the interface
- make offscreencanvas() only available for bindings

BUG=

Review-Url: https://codereview.chromium.org/2862923002
Cr-Commit-Position: refs/heads/master@{#469500}

third_party/WebKit/Source/modules/canvas2d/CanvasRenderingContext2D.cpp

@@ -586,19 +586,19 @@ void CanvasRenderingContext2D::ResourceElementChanged() {
 }
 
 bool CanvasRenderingContext2D::OriginClean() const {
-  return canvas()->OriginClean();
+  return host()->OriginClean();
 }
 
 void CanvasRenderingContext2D::SetOriginTainted() {
-  return canvas()->SetOriginTainted();
+  return host()->SetOriginTainted();
 }
 
 int CanvasRenderingContext2D::Width() const {
-  return canvas()->width();
+  return host()->Size().Width();
 }
 
 int CanvasRenderingContext2D::Height() const {
-  return canvas()->height();
+  return host()->Size().Height();
 }
 
 bool CanvasRenderingContext2D::HasImageBuffer() const {

third_party/WebKit/Source/modules/canvas2d/CanvasRenderingContext2D.h

@@ -275,7 +275,6 @@ class MODULES_EXPORT CanvasRenderingContext2D final
   ListHashSet<String> font_lru_list_;
 };
 
-// TODO(fserb): remove this?
 DEFINE_TYPE_CASTS(CanvasRenderingContext2D,
                   CanvasRenderingContext,
                   context,

third_party/WebKit/Source/modules/offscreencanvas2d/OffscreenCanvasRenderingContext2D.h

@@ -37,7 +37,7 @@ class MODULES_EXPORT OffscreenCanvasRenderingContext2D final
     }
   };
 
-  OffscreenCanvas* offscreenCanvas() const {
+  OffscreenCanvas* offscreenCanvasForBinding() const {
     DCHECK(!host() || host()->IsOffscreenCanvas());
     return static_cast<OffscreenCanvas*>(host());
   }
@@ -119,7 +119,6 @@ class MODULES_EXPORT OffscreenCanvasRenderingContext2D final
   CanvasPixelFormat PixelFormat() const override;
 };
 
-// TODO(fserb): remove this.
 DEFINE_TYPE_CASTS(OffscreenCanvasRenderingContext2D,
                   CanvasRenderingContext,
                   context,

third_party/WebKit/Source/modules/offscreencanvas2d/OffscreenCanvasRenderingContext2D.idl

@@ -9,7 +9,7 @@
     RuntimeEnabled=ExperimentalCanvasFeatures,
 ] interface OffscreenCanvasRenderingContext2D {
     // back-reference to the canvas
-    [ImplementedAs=offscreenCanvas] readonly attribute OffscreenCanvas canvas;
+    [ImplementedAs=offscreenCanvasForBinding] readonly attribute OffscreenCanvas canvas;
 
     [CallWith=ScriptState, RaisesException] Promise commit();