make alpha read back of bgra/rgba work

src/gpu/gl/GrGLCaps.cpp

 /*
  * Copyright 2012 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 
 #include "GrGLCaps.h"
 
@@ skipping 979 matching lines @@
     GR_GL_GetIntegerv(intf,
                       GR_GL_IMPLEMENTATION_COLOR_READ_TYPE,
                       &otherType);
 
     return (GrGLenum)otherFormat == format && (GrGLenum)otherType == type;
 }
 
 bool GrGLCaps::readPixelsSupported(const GrGLInterface* intf,
                                    GrGLenum format,
                                    GrGLenum type,
-                                   GrGLenum currFboFormat) const {
-    ReadPixelsSupportedFormat key = {format, type, currFboFormat};
+                                   GrPixelConfig currRTConfig) const {
+    ReadPixelsSupportedFormat key = {format, type, currRTConfig};
     if (const bool* supported = fReadPixelsSupportedCache.find(key)) {
         return *supported;
     }
     bool supported = this->doReadPixelsSupported(intf, format, type);
     fReadPixelsSupportedCache.set(key, supported);
     return supported;
 }
 
 void GrGLCaps::initFSAASupport(const GrGLContextInfo& ctxInfo, const GrGLInterface* gli) {
 
@@ skipping 336 matching lines @@
     glslCaps->fConfigSwizzle[kR11_EAC_GrPixelConfig] = "rrrr";
     glslCaps->fConfigSwizzle[kASTC_12x12_GrPixelConfig] = "rgba";
     glslCaps->fConfigSwizzle[kRGBA_float_GrPixelConfig] = "rgba";
     glslCaps->fConfigSwizzle[kRGBA_half_GrPixelConfig] = "rgba";
 
 }
 
 void GrGLCaps::onApplyOptionsOverrides(const GrContextOptions& options) {}