Make gpu work in iOS SampleApp.

This includes updates to the GrGLInterface and changes to the DeviceManager subclass used on iOS.
Review URL: https://codereview.appspot.com/6582043

git-svn-id: http://skia.googlecode.com/svn/trunk@5722 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/gyp/gpu.gyp b/gyp/gpu.gyp
index 10f1a80..94988ad 100644
--- a/gyp/gpu.gyp
+++ b/gyp/gpu.gyp
@@ -237,7 +237,7 @@
             '../src/gpu/gl/mesa/GrGLCreateMesaInterface.cpp',
           ],
         }],
-        [ 'skia_os == "win"', {
+        [ 'skia_os in ["win", "ios"]', {
           'sources!': [
             '../src/gpu/gl/GrGLDefaultInterface_none.cpp',
             '../src/gpu/gl/GrGLCreateNativeInterface_none.cpp',