Revert "Revert "Add a flag to GrSurfaceFlags that requires the texture to be cleared upon creation. ""

This reverts commit a9e795eab5f59a52d96b8fdc39351452835f5eb9.

Bug: skia:
Change-Id: Ibfc51497ae99f332f8f72a799393a1b2996f7f3f
Reviewed-on: https://skia-review.googlesource.com/17767
Reviewed-by: Brian Osman <brianosman@google.com>
Commit-Queue: Brian Salomon <bsalomon@google.com>
diff --git a/include/gpu/gl/GrGLInterface.h b/include/gpu/gl/GrGLInterface.h
index c84eca2..e5479eb 100644
--- a/include/gpu/gl/GrGLInterface.h
+++ b/include/gpu/gl/GrGLInterface.h
@@ -125,6 +125,8 @@
         GrGLFunction<GrGLClearProc> fClear;
         GrGLFunction<GrGLClearColorProc> fClearColor;
         GrGLFunction<GrGLClearStencilProc> fClearStencil;
+        GrGLFunction<GrGLClearTexImageProc> fClearTexImage;
+        GrGLFunction<GrGLClearTexSubImageProc> fClearTexSubImage;
         GrGLFunction<GrGLColorMaskProc> fColorMask;
         GrGLFunction<GrGLCompileShaderProc> fCompileShader;
         GrGLFunction<GrGLCompressedTexImage2DProc> fCompressedTexImage2D;