make alpha read back of bgra/rgba work

src/gpu/gl/GrGLCaps.h

 /*
  * Copyright 2012 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 
 #ifndef GrGLCaps_DEFINED
 #define GrGLCaps_DEFINED
@@ skipping 217 matching lines @@
 
     /// Use indices or vertices in CPU arrays rather than VBOs for dynamic content.
     bool useNonVBOVertexAndIndexDynamicData() const {
         return fUseNonVBOVertexAndIndexDynamicData;
     }
 
     /// Does ReadPixels support the provided format/type combo?
     bool readPixelsSupported(const GrGLInterface* intf,
                              GrGLenum format,
                              GrGLenum type,
-                             GrGLenum currFboFormat) const;
+                             GrPixelConfig currRTConfig) const;
 
     bool isCoreProfile() const { return fIsCoreProfile; }
 
     bool bindFragDataLocationSupport() const { return fBindFragDataLocationSupport; }
 
     bool bindUniformLocationSupport() const { return fBindUniformLocationSupport; }
 
     /// Are textures with GL_TEXTURE_EXTERNAL_OES type supported.
     bool externalTextureSupport() const { return fExternalTextureSupport; }
 
@@ skipping 122 matching lines @@
     bool fUseNonVBOVertexAndIndexDynamicData : 1;
     bool fIsCoreProfile : 1;
     bool fBindFragDataLocationSupport : 1;
     bool fSRGBWriteControl : 1;
     bool fRGBA8888PixelsOpsAreSlow : 1;
     bool fPartialFBOReadIsSlow : 1;
     bool fBindUniformLocationSupport : 1;
     bool fExternalTextureSupport : 1;
 
     struct ReadPixelsSupportedFormat {
-        GrGLenum fFormat;
-        GrGLenum fType;
-        GrGLenum fFboFormat;
+        ReadPixelsSupportedFormat() { memset(this, 0, sizeof(ReadPixelsSupportedFormat)); }
+        ReadPixelsSupportedFormat(GrGLenum format, GrGLenum type, GrPixelConfig rtConfig) {
+            memset(this, 0, sizeof(ReadPixelsSupportedFormat));
+            fFormat = format;
+            fType = type;
+            fRTConfig = rtConfig;
+        }
+
+        GrGLenum        fFormat;
+        GrGLenum        fType;
+        GrPixelConfig   fRTConfig;
 
         bool operator==(const ReadPixelsSupportedFormat& rhs) const {
             return fFormat    == rhs.fFormat
                 && fType      == rhs.fType
-                && fFboFormat == rhs.fFboFormat;
+                && fRTConfig  == rhs.fRTConfig;
         }
     };
     mutable SkTHashMap<ReadPixelsSupportedFormat, bool> fReadPixelsSupportedCache;
 
     typedef GrCaps INHERITED;
 };
 
 #endif