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

skia/skia.gyp

Index: skia/skia.gyp
===================================================================
--- skia/skia.gyp	(revision 167659)
+++ skia/skia.gyp	(working copy)
@@ -170,10 +170,6 @@
         'ext/SkThread_chrome.cc',
         'ext/platform_canvas.cc',
         'ext/platform_canvas.h',
-        'ext/platform_canvas_linux.cc',
-        'ext/platform_canvas_mac.cc',
-        'ext/platform_canvas_skia.cc',
-        'ext/platform_canvas_win.cc',
         'ext/platform_device.cc',
         'ext/platform_device.h',
         'ext/platform_device_linux.cc',
@@ -378,15 +374,6 @@
             '../third_party/skia/src/ports/SkFontHost_FreeType_common.cpp',
           ],
         }],
-        [ 'use_aura == 1 and use_canvas_skia == 1', {
-          'sources/': [
-            ['exclude', 'ext/platform_canvas_mac\\.cc$'],
-            ['exclude', 'ext/platform_canvas_linux\\.cc$'],
-            ['exclude', 'ext/platform_canvas_win\\.cc$'],
-          ],
-        }, { # use_aura == 0 and use_canvas_skia == 1
-          'sources/': [ ['exclude', 'ext/platform_canvas_skia\\.cc$'] ],
-        }],
         [ 'toolkit_uses_gtk == 1', {
           'dependencies': [
             '../build/linux/system.gyp:gdk',
@@ -428,7 +415,6 @@
               ],
               'sources/': [
                 ['include', 'ext/platform_device_linux\\.cc$'],
-                ['include', 'ext/platform_canvas_linux\\.cc$'],
                 ['exclude', '../third_party/skia/src/pdf/'],
               ],
               'sources!': [
@@ -446,7 +432,6 @@
             [ '_toolset=="host" and host_os=="linux"', {
               'sources': [
                 'ext/platform_device_linux.cc',
-                'ext/platform_canvas_linux.cc',
               ],
             }],
           ],