aura: Use platform independent skia::PlatformCanvas when possible.

skia/skia.gyp

Index: skia/skia.gyp
diff --git a/skia/skia.gyp b/skia/skia.gyp
index 82ababb4353b3b451a75c3300fa13e06d1cd7766..5f67d24e6b34d4ec1658d8626bedac25a3edf226 100644
--- a/skia/skia.gyp
+++ b/skia/skia.gyp
@@ -712,6 +712,7 @@
         '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',
@@ -855,6 +856,14 @@
             ['include', 'ext/platform_canvas_linux\\.cc$'],
           ],
         }],
+        [ 'use_aura == 1', {
+          'sources/': [
+            ['exclude', 'ext/platform_canvas_mac\\.cc$'],
+            ['exclude', 'ext/platform_canvas_linux\\.cc$'],
+            ['exclude', 'ext/platform_canvas_win\\.cc$'],
+            ['include', 'ext/platform_canvas_skia\\.cc$'],

[piman, 2012/03/21 16:54:19]

Unless I missed something, this will compile and link platform_canvas_skia.cc on
all platforms which I don't think is what you want (see also your trybot error).
You don't need the 'include' line (since nothing else is explicitly excluding
it), but you can add a second stance in this condition block (the 'else' clause)
that excludes it.

[ 'use_aura==1' {
'sources/': [
  ['exclude', 'ext/platform_canvas_mac\\.cc$'],
  ['exclude', 'ext/platform_canvas_linux\\.cc$'],
  ['exclude', 'ext/platform_canvas_win\\.cc$'],
]
}, {
'sources/': [
  ['exclude', 'ext/platform_canvas_skia\\.cc$'],
]
}]

+          ],
+        }],
         [ 'toolkit_uses_gtk == 1', {
           'dependencies': [
             '../build/linux/system.gyp:gdk',