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

webkit/glue/webkit_glue.h

Index: webkit/glue/webkit_glue.h
===================================================================
--- webkit/glue/webkit_glue.h	(revision 167659)
+++ webkit/glue/webkit_glue.h	(working copy)
@@ -21,15 +21,12 @@
 #include "webkit/glue/webkit_glue_export.h"
 
 class SkBitmap;
+class SkCanvas;
 
 namespace net {
 class URLRequest;
 }
 
-namespace skia {
-class PlatformCanvas;
-}
-
 namespace WebKit {
 struct WebFileInfo;
 class WebFrame;
@@ -99,7 +96,7 @@
     WebKit::WebFileInfo* web_file_info);
 
 // Returns a WebCanvas pointer associated with the given Skia canvas.
-WEBKIT_GLUE_EXPORT WebKit::WebCanvas* ToWebCanvas(skia::PlatformCanvas*);
+WEBKIT_GLUE_EXPORT WebKit::WebCanvas* ToWebCanvas(SkCanvas*);
 
 // Returns the number of currently-active glyph pages this process is using.
 // There can be many such pages (maps of 256 character -> glyph) so this is