Adding optimization to avoid image copy in SkSurface copy on write when content is discardable

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 104 matching lines @@
 
 #else
     #define CHECK_LOCKCOUNT_BALANCE(bitmap)
     #define CHECK_SHADER_NOSETCONTEXT(paint)
 #endif
 
 typedef SkTLazy<SkPaint> SkLazyPaint;
 
 void SkCanvas::predrawNotify() {
     if (fSurfaceBase) {
-        fSurfaceBase->aboutToDraw();
+        fSurfaceBase->aboutToDraw(SkSurface::kRetain_ContentChangeMode);
     }
 }
 
 ///////////////////////////////////////////////////////////////////////////////
 
 /*  This is the record we keep for each SkDevice that the user installs.
     The clip/matrix/proc are fields that reflect the top of the save/restore
     stack. Whenever the canvas changes, it marks a dirty flag, and then before
     these are used (assuming we're not on a layer) we rebuild these cache
     values: they reflect the top of the save stack, but translated and clipped
@@ skipping 1992 matching lines @@
     return *paint;
 }
 
 const SkRegion& SkCanvas::LayerIter::clip() const { return fImpl->getClip(); }
 int SkCanvas::LayerIter::x() const { return fImpl->getX(); }
 int SkCanvas::LayerIter::y() const { return fImpl->getY(); }
 
 ///////////////////////////////////////////////////////////////////////////////
 
 SkCanvas::ClipVisitor::~ClipVisitor() { }