make allocPixels throw on failure

src/core/SkPictureShader.cpp

 /*
  * Copyright 2014 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkPictureShader.h"
 
 #include "SkBitmap.h"
@@ skipping 89 matching lines @@
     }
 
     // The actual scale, compensating for rounding & clamping.
     SkSize tileScale = SkSize::Make(SkIntToScalar(tileSize.width()) / fTile.width(),
                                     SkIntToScalar(tileSize.height()) / fTile.height());
 
     SkAutoMutexAcquire ama(fCachedBitmapShaderMutex);
 
     if (!fCachedBitmapShader || tileScale != fCachedTileScale) {
         SkBitmap bm;
-        if (!bm.allocN32Pixels(tileSize.width(), tileSize.height())) {
+        if (!bm.tryAllocN32Pixels(tileSize.width(), tileSize.height())) {
             return NULL;
         }
         bm.eraseColor(SK_ColorTRANSPARENT);
 
         SkCanvas canvas(bm);
         canvas.scale(tileScale.width(), tileScale.height());
         canvas.translate(fTile.x(), fTile.y());
         canvas.drawPicture(fPicture);
 
         fCachedTileScale = tileScale;
@@ skipping 101 matching lines @@
     return bitmapShader->asNewEffect(context, paint, NULL, paintColor, effect);
 }
 #else
 bool SkPictureShader::asNewEffect(GrContext* context, const SkPaint& paint,
                                   const SkMatrix* localMatrix, GrColor* paintColor,
                                   GrEffect** effect) const {
     SkDEBUGFAIL("Should not call in GPU-less build");
     return false;
 }
 #endif