Add discard API to SkCanvas, plumb it to glDiscardFramebuffer()

src/core/SkCanvas.cpp

 
 /*
  * Copyright 2008 The Android Open Source Project
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 
 #include "SkCanvas.h"
@@ skipping 1894 matching lines @@
 //////////////////////////////////////////////////////////////////////////////
 
 void SkCanvas::clear(SkColor color) {
     SkDrawIter  iter(this);
     this->predrawNotify();
     while (iter.next()) {
         iter.fDevice->clear(color);
     }
 }
 
+void SkCanvas::onDiscard() {
+    if (NULL != fSurfaceBase) {
+        fSurfaceBase->aboutToDraw(SkSurface::kDiscard_ContentChangeMode);
+    }
+}
+
 void SkCanvas::drawPaint(const SkPaint& paint) {
     this->internalDrawPaint(paint);
 }
 
 void SkCanvas::internalDrawPaint(const SkPaint& paint) {
     CHECK_SHADER_NOSETCONTEXT(paint);
 
     LOOPER_BEGIN(paint, SkDrawFilter::kPaint_Type, NULL)
 
     while (iter.next()) {
@@ skipping 717 matching lines @@
     if (!bitmap.installPixels(info, pixels, rowBytes)) {
         return NULL;
     }
 
     // should this functionality be moved into allocPixels()?
     if (!bitmap.info().isOpaque()) {
         bitmap.eraseColor(0);
     }
     return SkNEW_ARGS(SkCanvas, (bitmap));
 }