Don't allow renderTarget==NULL to GrContext::clear() and friends.

src/effects/SkMorphologyImageFilter.cpp

Index: src/effects/SkMorphologyImageFilter.cpp
diff --git a/src/effects/SkMorphologyImageFilter.cpp b/src/effects/SkMorphologyImageFilter.cpp
index 05fc1fdb211fc028ccea6a1a2ee61ac2d6238b76..72c98dd97eaa1592ee7aeb5ef5e60ac20858f4f1 100644
--- a/src/effects/SkMorphologyImageFilter.cpp
+++ b/src/effects/SkMorphologyImageFilter.cpp
@@ -530,9 +530,10 @@ bool apply_morphology(const SkBitmap& input,
                               morphType, Gr1DKernelEffect::kX_Direction);
         SkIRect clearRect = SkIRect::MakeXYWH(dstRect.fLeft, dstRect.fBottom,
                                               dstRect.width(), radius.fHeight);
-        context->clear(&clearRect, GrMorphologyEffect::kErode_MorphologyType == morphType ?
-                                   SK_ColorWHITE :
-                                   SK_ColorTRANSPARENT, false);
+        GrColor clearColor = GrMorphologyEffect::kErode_MorphologyType == morphType ?
+                                SK_ColorWHITE :
+                                SK_ColorTRANSPARENT;
+        context->clear(&clearRect, clearColor, false, texture->asRenderTarget());
         srcTexture.reset(texture);
         srcRect = dstRect;
     }