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

src/gpu/SkGpuDevice.cpp

 /*
  * Copyright 2011 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkGpuDevice.h"
 
 #include "effects/GrBicubicEffect.h"
@@ skipping 640 matching lines @@
     GrTexture* mask = context->refScratchTexture(desc,GrContext::kApprox_ScratchTexMatch);
     if (NULL == mask) {
         return NULL;
     }
 
     SkRect clipRect = SkRect::MakeWH(maskRect.width(), maskRect.height());
 
     GrContext::AutoRenderTarget art(context, mask->asRenderTarget());
     GrContext::AutoClip ac(context, clipRect);
 
-    context->clear(NULL, 0x0, true);
+    context->clear(NULL, 0x0, true, mask->asRenderTarget());
 
     GrPaint tempPaint;
     if (doAA) {
         tempPaint.setAntiAlias(true);
         // AA uses the "coverage" stages on GrDrawTarget. Coverage with a dst
         // blend coeff of zero requires dual source blending support in order
         // to properly blend partially covered pixels. This means the AA
         // code path may not be taken. So we use a dst blend coeff of ISA. We
         // could special case AA draws to a dst surface with known alpha=0 to
         // use a zero dst coeff when dual source blending isn't available.
@@ skipping 1180 matching lines @@
     return true;
 }
 
 SkImageFilter::Cache* SkGpuDevice::getImageFilterCache() {
     // We always return a transient cache, so it is freed after each
     // filter traversal.
     return SkImageFilter::Cache::Create(kDefaultImageFilterCacheSize);
 }
 
 #endif