Add ability to extract YUV planes from SkImage

include/core/SkImageInfo.h

 /*
  * Copyright 2013 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef SkImageInfo_DEFINED
 #define SkImageInfo_DEFINED
 
@@ skipping 188 matching lines @@
     static SkImageInfo MakeN32Premul(const SkISize& size,
                                      SkColorProfileType pt = kLinear_SkColorProfileType) {
         return MakeN32Premul(size.width(), size.height(), pt);
     }
 
     static SkImageInfo MakeA8(int width, int height) {
         return SkImageInfo(width, height, kAlpha_8_SkColorType, kPremul_SkAlphaType,
                            kLinear_SkColorProfileType);
     }
 
+    static SkImageInfo MakeGray8(int width, int height) {
+        return SkImageInfo(width, height, kGray_8_SkColorType, kPremul_SkAlphaType,
+                           kLinear_SkColorProfileType);
+    }
+
     static SkImageInfo MakeUnknown(int width, int height) {
         return SkImageInfo(width, height, kUnknown_SkColorType, kUnknown_SkAlphaType,
                            kLinear_SkColorProfileType);
     }
 
     static SkImageInfo MakeUnknown() {
         return SkImageInfo();
     }
 
     int width() const { return fWidth; }
@@ skipping 90 matching lines @@
     SkImageInfo(int width, int height, SkColorType ct, SkAlphaType at, SkColorProfileType pt)
         : fWidth(width)
         , fHeight(height)
         , fColorType(ct)
         , fAlphaType(at)
         , fProfileType(pt)
     {}
 };
 
 #endif