check (runtime) for null-pixels even when lock succeeds

src/core/SkMipMap.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 "SkMipMap.h"
 #include "SkBitmap.h"
 #include "SkColorPriv.h"
@@ skipping 221 matching lines @@
     size_t storageSize = SkMipMap::AllocLevelsSize(countLevels, size);
     if (0 == storageSize) {
         return NULL;
     }
 
     SkAutoPixmapUnlock srcUnlocker;
     if (!src.requestLock(&srcUnlocker)) {
         return NULL;
     }
     const SkPixmap& srcPixmap = srcUnlocker.pixmap();
+    // Try to catch where we might have returned NULL for src crbug.com/492818
+    if (NULL == srcPixmap.addr()) {
+        sk_throw();
+    }
 
     SkMipMap* mipmap;
     if (fact) {
         SkDiscardableMemory* dm = fact(storageSize);
         if (NULL == dm) {
             return NULL;
         }
         mipmap = SkNEW_ARGS(SkMipMap, (storageSize, dm));
     } else {
         mipmap = SkNEW_ARGS(SkMipMap, (sk_malloc_throw(storageSize), storageSize));
@@ skipping 88 matching lines @@
     }
 
     if (level > fCount) {
         level = fCount;
     }
     if (levelPtr) {
         *levelPtr = fLevels[level - 1];
     }
     return true;
 }