Add can-ignore-rect hint to clear call

src/gpu/gl/GrGLCaps.h

Index: src/gpu/gl/GrGLCaps.h
===================================================================
--- src/gpu/gl/GrGLCaps.h	(revision 12054)
+++ src/gpu/gl/GrGLCaps.h	(working copy)
@@ -248,6 +248,8 @@
     /// Is there support for discarding the frame buffer
     bool discardFBSupport() const { return fDiscardFBSupport; }
 
+    bool fullClearIsFree() const { return fFullClearIsFree; }
+
 private:
     /**
      * Maintains a bit per GrPixelConfig. It is used to avoid redundantly
@@ -329,6 +331,7 @@
     bool fIsCoreProfile : 1;
     bool fFixedFunctionSupport : 1;
     bool fDiscardFBSupport : 1;
+    bool fFullClearIsFree : 1;
 
     typedef GrDrawTargetCaps INHERITED;
 };