Add ability to query read pixels support without a render target.

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 268 matching lines @@
 
     /// Is there support for ES2 compatability?
     bool ES2CompatibilitySupport() const { return fES2CompatibilitySupport; }
 
     /// Can we call glDisable(GL_MULTISAMPLE)?
     bool multisampleDisableSupport() const { return fMultisampleDisableSupport; }
 
     /// 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(GrGLRenderTarget* target,
+    /// Does ReadPixels support reading readConfig pixels from a FBO that is renderTargetConfig?
+    bool readPixelsSupported(GrPixelConfig renderTargetConfig,
                              GrPixelConfig readConfig,
                              std::function<void (GrGLenum, GrGLint*)> getIntegerv,
-                             std::function<void (GrGLRenderTarget*)> bindRenderTarget) const;
+                             std::function<bool ()> bindRenderTarget) 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 152 matching lines @@
 
         GrSwizzle fSwizzle;
     };
 
     ConfigInfo fConfigTable[kGrPixelConfigCnt];
 
     typedef GrCaps INHERITED;
 };
 
 #endif