allow canvas to force conservative clips (for speed)

src/core/SkDeviceLooper.cpp

 /*
  * Copyright 2013 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkDeviceLooper.h"
 
 SkDeviceLooper::SkDeviceLooper(const SkBitmap& base,
                                const SkRasterClip& rc,
                                const SkIRect& bounds, bool aa)
-: fBaseBitmap(base)
-, fBaseRC(rc)
-, fDelta(aa ? kAA_Delta : kBW_Delta)
+    : fBaseBitmap(base)
+    , fBaseRC(rc)
+    , fSubsetRC(rc.isForceConservativeRects())
+    , fDelta(aa ? kAA_Delta : kBW_Delta)
 {
     // sentinels that next() has not yet been called, and so our mapper functions
     // should not be called either.
     fCurrBitmap = NULL;
     fCurrRC = NULL;
 
     if (!rc.isEmpty()) {
         // clip must be contained by the bitmap
         SkASSERT(SkIRect::MakeWH(base.width(), base.height()).contains(rc.getBounds()));
     }
@@ skipping 96 matching lines @@
             while (next_tile(fClippedBounds, fDelta, &fCurrOffset)) {
                 if (this->computeCurrBitmapAndClip()) {
                     return true;
                 }
             }
             break;
     }
     fState = kDone_State;
     return false;
 }