Move some work from backend onClear to base class clear

src/gpu/GrReorderCommandBuilder.cpp

 /*
  * Copyright 2015 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "GrReorderCommandBuilder.h"
 
 template <class Left, class Right>
@@ skipping 14 matching lines @@
     int i = 0;
     batch->setPipeline(state->getPipeline());
     GrRenderTarget* rt = state->getPipeline()->getRenderTarget();
     if (!this->cmdBuffer()->empty()) {
         GrTargetCommands::CmdBuffer::ReverseIter reverseIter(*this->cmdBuffer());
 
         do {
             if (Cmd::kDrawBatch_CmdType == reverseIter->type()) {
                 DrawBatch* previous = static_cast<DrawBatch*>(reverseIter.get());
 
-                // We cannot continue to search backwards if the render target changes
                 if (previous->fBatch->pipeline()->getRenderTarget() != rt) {
                     break;
                 }
-
+                // We cannot continue to search backwards if the render target changes
                 if (previous->fBatch->combineIfPossible(batch)) {
                     return NULL;
                 }
 
                 if (intersect(previous->fBatch->bounds(), batch->bounds())) {
                     break;
                 }
             } else if (Cmd::kClear_CmdType == reverseIter->type()) {
                 Clear* previous = static_cast<Clear*>(reverseIter.get());
 
+                if (previous->renderTarget() != rt) {
+                    break;
+                }
                 // We set the color to illegal if we are doing a discard.
-                // If we can ignore the rect, then we do a full clear
                 if (previous->fColor == GrColor_ILLEGAL ||
-                    previous->fCanIgnoreRect ||
                     intersect(batch->bounds(), previous->fRect)) {
                     break;
                 }
             } else {
                 // TODO temporary until we can navigate the other types of commands
                 break;
             }
         } while (reverseIter.previous() && ++i < kMaxLookback);
     }
 
     return GrNEW_APPEND_TO_RECORDER(*this->cmdBuffer(), DrawBatch, (state, batch,
                                                                     this->batchTarget()));
 }