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

src/gpu/GrInOrderDrawBuffer.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 "GrInOrderDrawBuffer.h"
 
 #include "GrBufferAllocPool.h"
@@ skipping 432 matching lines @@
         renderTarget = this->drawState()->getRenderTarget();
         SkASSERT(renderTarget);
     }
     ClearStencilClip* clr = GrNEW_APPEND_TO_RECORDER(fCmdBuffer, ClearStencilClip, (renderTarget));
     clr->fRect = rect;
     clr->fInsideClip = insideClip;
     this->recordTraceMarkersIfNecessary();
 }
 
 void GrInOrderDrawBuffer::discard(GrRenderTarget* renderTarget) {
+    SkASSERT(renderTarget);
     if (!this->caps()->discardRenderTargetSupport()) {
         return;
     }
-    if (NULL == renderTarget) {
-        renderTarget = this->drawState()->getRenderTarget();
-        SkASSERT(renderTarget);
-    }
     Clear* clr = GrNEW_APPEND_TO_RECORDER(fCmdBuffer, Clear, (renderTarget));
     clr->fColor = GrColor_ILLEGAL;
     this->recordTraceMarkersIfNecessary();
 }
 
 void GrInOrderDrawBuffer::reset() {
     SkASSERT(1 == fGeoPoolStateStack.count());
     this->resetVertexSource();
     this->resetIndexSource();
 
@@ skipping 389 matching lines @@
         fCmdBuffer.back().fType = add_trace_bit(fCmdBuffer.back().fType);
         fGpuCmdMarkers.push_back(activeTraceMarkers);
     }
 }
 
 void GrInOrderDrawBuffer::clipWillBeSet(const GrClipData* newClipData) {
     INHERITED::clipWillBeSet(newClipData);
     fClipSet = true;
     fClipProxyState = kUnknown_ClipProxyState;
 }