Add a full clear method to GrDrawTarget.

src/gpu/GrDrawContext.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 "GrBatchTest.h"
 #include "GrColor.h"
 #include "GrDrawContext.h"
@@ skipping 185 matching lines @@
                           bool canIgnoreRect) {
     ASSERT_SINGLE_OWNER
     RETURN_IF_ABANDONED
     SkDEBUGCODE(this->validate();)
     GR_AUDIT_TRAIL_AUTO_FRAME(fAuditTrail, "GrDrawContext::clear");
 
     AutoCheckFlush acf(fDrawingManager);
 
     const SkIRect rtRect = SkIRect::MakeWH(this->width(), this->height());
     SkIRect clippedRect;
+    bool isFull = false;
     if (!rect ||
         (canIgnoreRect && fContext->caps()->fullClearIsFree()) ||
         rect->contains(rtRect)) {
         rect = &rtRect;
+        isFull = true;
     } else {
         clippedRect = *rect;
         if (!clippedRect.intersect(rtRect)) {
             return;
         }
         rect = &clippedRect;
     }
 
     if (fContext->caps()->useDrawInsteadOfClear()) {
         // This works around a driver bug with clear by drawing a rect instead.
         // The driver will ignore a clear if it is the only thing rendered to a
         // target before the target is read.
         if (rect == &rtRect) {
             this->discard();
         }
 
         GrPaint paint;
         paint.setColor4f(GrColor4f::FromGrColor(color));
         paint.setXPFactory(GrPorterDuffXPFactory::Make(SkXfermode::kSrc_Mode));
 
         this->drawRect(GrNoClip(), paint, SkMatrix::I(), SkRect::Make(*rect));
+    } else if (isFull) {
+        this->getDrawTarget()->fullClear(this->accessRenderTarget(), color);
     } else {
         sk_sp<GrBatch> batch = GrClearBatch::Make(*rect, color, this->accessRenderTarget());
         this->getDrawTarget()->addBatch(std::move(batch));
     }
 }
 
 
 void GrDrawContext::drawPaint(const GrClip& clip,
                               const GrPaint& origPaint,
                               const SkMatrix& viewMatrix) {
@@ skipping 1062 matching lines @@
 
 void GrDrawContext::drawBatch(const GrPipelineBuilder& pipelineBuilder, const GrClip& clip,
                               GrDrawBatch* batch) {
     ASSERT_SINGLE_OWNER
     RETURN_IF_ABANDONED
     SkDEBUGCODE(this->validate();)
     GR_AUDIT_TRAIL_AUTO_FRAME(fAuditTrail, "GrDrawContext::drawBatch");
 
     this->getDrawTarget()->drawBatch(pipelineBuilder, this, clip, batch);
 }