Remove GrTexture::releaseRenderTarget() and add GrSurface::isSameAs().

include/gpu/GrRenderTarget.h

Index: include/gpu/GrRenderTarget.h
===================================================================
--- include/gpu/GrRenderTarget.h	(revision 8517)
+++ include/gpu/GrRenderTarget.h	(working copy)
@@ -149,15 +149,6 @@
     }
 
     friend class GrTexture;
-    // When a texture unrefs an owned render target this func
-    // removes the back pointer. This could be called from
-    // texture's destructor but would have to be done in derived
-    // classes. By the time of texture base destructor it has already
-    // lost its pointer to the rt.
-    void onTextureReleaseRenderTarget() {
-        GrAssert(NULL != fTexture);
-        fTexture = NULL;
-    }
 
     // override of GrResource
     virtual void onAbandon() SK_OVERRIDE;