make allocPixels throw on failure

src/images/SkImageDecoder_libpng.cpp

 /*
  * Copyright 2006 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 "SkImageDecoder.h"
 #include "SkImageEncoder.h"
 #include "SkColor.h"
@@ skipping 805 matching lines @@
     int w = rect.width() / sampleSize;
     int h = rect.height() / sampleSize;
     const bool swapOnly = (rect == region) && (w == decodedBitmap.width()) &&
                           (h == decodedBitmap.height()) && bm->isNull();
     const bool needColorTable = kIndex_8_SkColorType == colorType;
     if (swapOnly) {
         if (!this->allocPixelRef(&decodedBitmap, needColorTable ? colorTable : NULL)) {
             return false;
         }
     } else {
-        if (!decodedBitmap.allocPixels(NULL, needColorTable ? colorTable : NULL)) {
+        if (!decodedBitmap.tryAllocPixels(NULL, needColorTable ? colorTable : NULL)) {
             return false;
         }
     }
     SkAutoLockPixels alp(decodedBitmap);
 
     /* Turn on interlace handling.  REQUIRED if you are not using
     * png_read_image().  To see how to handle interlacing passes,
     * see the png_read_row() method below:
     */
     const int number_passes = (interlaceType != PNG_INTERLACE_NONE) ?
@@ skipping 441 matching lines @@
     return SkImageDecoder::kUnknown_Format;
 }
 
 SkImageEncoder* sk_libpng_efactory(SkImageEncoder::Type t) {
     return (SkImageEncoder::kPNG_Type == t) ? SkNEW(SkPNGImageEncoder) : NULL;
 }
 
 static SkImageDecoder_DecodeReg gDReg(sk_libpng_dfactory);
 static SkImageDecoder_FormatReg gFormatReg(get_format_png);
 static SkImageEncoder_EncodeReg gEReg(sk_libpng_efactory);