Simplify platform_canvas.h by recognizing that PlatformCanvas does not actually extend

skia/ext/platform_canvas_mac.cc

 // Copyright (c) 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "skia/ext/platform_canvas.h"
 
 #include "base/debug/trace_event.h"
 #include "skia/ext/bitmap_platform_device.h"
 #include "third_party/skia/include/core/SkTypes.h"
 
 namespace skia {
-
+#if 0
 PlatformCanvas::PlatformCanvas(int width, int height, bool is_opaque) {
   TRACE_EVENT2("skia", "PlatformCanvas::PlatformCanvas",
                "width", width, "height", height);
   initialize(width, height, is_opaque);
 }
 
 PlatformCanvas::PlatformCanvas(int width,
                                int height,
                                bool is_opaque,
                                CGContextRef context) {
@@ skipping 22 matching lines @@
       data, width, height, is_opaque));
 }
 
 bool PlatformCanvas::initialize(CGContextRef context,
                                 int width,
                                 int height,
                                 bool is_opaque) {
   return initializeWithDevice(BitmapPlatformDevice::Create(
       context, width, height, is_opaque));
 }
-
+#endif
 }  // namespace skia