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

content/renderer/browser_plugin/browser_plugin.cc

Index: content/renderer/browser_plugin/browser_plugin.cc
===================================================================
--- content/renderer/browser_plugin/browser_plugin.cc	(revision 165342)
+++ content/renderer/browser_plugin/browser_plugin.cc	(working copy)
@@ -693,7 +693,7 @@
     return;
   }
 
-  const size_t stride = skia::PlatformCanvas::StrideForWidth(window_rect.width);
+  const size_t stride = skia::PlatformCanvasStrideForWidth(window_rect.width);
   // Make sure the size of the damage buffer is at least four bytes so that we
   // can fit in a magic word to verify that the memory is shared correctly.
   size_t size =