Remove unused gfx::Canvas API

ui/gfx/canvas.cc

Index: ui/gfx/canvas.cc
diff --git a/ui/gfx/canvas.cc b/ui/gfx/canvas.cc
index 49e32350a42e45c8c498aa7cd00534f6c578b4fb..da4911b7c2955f27ac707e7922037f611857ecea 100644
--- a/ui/gfx/canvas.cc
+++ b/ui/gfx/canvas.cc
@@ -531,14 +531,6 @@ void Canvas::TileImageInt(const ImageSkia& image,
   canvas_->drawRect(dest_rect, paint);
 }
 
-NativeDrawingContext Canvas::BeginPlatformPaint() {
-  return skia::BeginPlatformPaint(canvas_);
-}
-
-void Canvas::EndPlatformPaint() {
-  skia::EndPlatformPaint(canvas_);
-}
-
 void Canvas::Transform(const gfx::Transform& transform) {
   canvas_->concat(transform.matrix());
 }