ui/gfx: Make gfx::Canvas inherit from gfx::CanvasSkia.

ui/gfx/canvas.cc

Index: ui/gfx/canvas.cc
diff --git a/ui/gfx/canvas.cc b/ui/gfx/canvas.cc
index 619f93f6f03fcef6fef6830bed41dba5b040a656..ee34da968be15c94371da17110848289b52ecc03 100644
--- a/ui/gfx/canvas.cc
+++ b/ui/gfx/canvas.cc
@@ -6,20 +6,20 @@
 
 namespace gfx {
 
-CanvasSkia* Canvas::AsCanvasSkia() {
-  return NULL;
+Canvas::Canvas()
+    : CanvasSkia() {
 }
 
-const CanvasSkia* Canvas::AsCanvasSkia() const {
-  return NULL;
+Canvas::Canvas(SkCanvas* canvas)
+    : CanvasSkia(canvas) {
 }
 
-SkCanvas* Canvas::GetSkCanvas() {
-  return NULL;
+Canvas::Canvas(const gfx::Size& size, bool is_opaque)
+    : CanvasSkia(size, is_opaque) {
 }
 
-const SkCanvas* Canvas::GetSkCanvas() const {
-  return NULL;
+Canvas::Canvas(const SkBitmap& bitmap, bool is_opaque)
+    : CanvasSkia(bitmap, is_opaque) {
 }
 
 }  // namespace gfx