make allocPixels throw on failure

tests/PathOpsSkpClipTest.cpp

 #include "CrashHandler.h"
 // #include "OverwriteLine.h"
 #include "Resources.h"
 #include "SkBitmap.h"
 #include "SkCanvas.h"
 #include "SkColor.h"
 #include "SkColorPriv.h"
 #include "SkCommandLineFlags.h"
 #include "SkDevice.h"
 #include "SkForceLinking.h"
@@ skipping 464 matching lines @@
         SkScalar width = pic->cullRect().width();
         SkScalar height = pic->cullRect().height();
         SkBitmap oldBitmap, opBitmap;
         fScale = 1;
         while (width / fScale > 32767 || height / fScale > 32767) {
             ++fScale;
         }
         do {
             int dimX = SkScalarCeilToInt(width / fScale);
             int dimY = SkScalarCeilToInt(height / fScale);
-            if (oldBitmap.allocN32Pixels(dimX, dimY) &&
-                opBitmap.allocN32Pixels(dimX, dimY)) {
+            if (oldBitmap.tryAllocN32Pixels(dimX, dimY) && opBitmap.tryAllocN32Pixels(dimX, dimY)) {
                 break;
             }
             SkDebugf("-%d-", fScale);
         } while (++fScale < 256);
         if (fScale >= 256) {
             SkDebugf("unable to allocate bitmap for %s (w=%f h=%f)\n", fFilename,
                     width, height);
             goto finish;
         }
         oldBitmap.eraseColor(SK_ColorWHITE);
@@ skipping 614 matching lines @@
     }
     SkGraphics::Term();
     return 0;
 }
 
 #if !defined(SK_BUILD_FOR_IOS) && !defined(SK_BUILD_FOR_NACL)
 int main(int argc, char * const argv[]) {
     return tool_main(argc, (char**) argv);
 }
 #endif