Add assertHeld() to SkMutex.

src/core/SkScaledImageCache.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 "SkScaledImageCache.h"
 #include "SkMipMap.h"
 #include "SkPixelRef.h"
@@ skipping 657 matching lines @@
 
 #include "SkThread.h"
 
 SK_DECLARE_STATIC_MUTEX(gMutex);
 static SkScaledImageCache* gScaledImageCache = NULL;
 static void cleanup_gScaledImageCache() { SkDELETE(gScaledImageCache); }
 
 /** Must hold gMutex when calling. */
 static SkScaledImageCache* get_cache() {
     // gMutex is always held when this is called, so we don't need to be fancy in here.
+    gMutex.assertHeld();
     if (NULL == gScaledImageCache) {
 #ifdef SK_USE_DISCARDABLE_SCALEDIMAGECACHE
         gScaledImageCache = SkNEW_ARGS(SkScaledImageCache, (SkDiscardableMemory::Create));
 #else
         gScaledImageCache = SkNEW_ARGS(SkScaledImageCache, (SK_DEFAULT_IMAGE_CACHE_LIMIT));
 #endif
         atexit(cleanup_gScaledImageCache);
     }
     return gScaledImageCache;
 }
@@ skipping 86 matching lines @@
     return SkScaledImageCache::GetBytesUsed();
 }
 
 size_t SkGraphics::GetImageCacheByteLimit() {
     return SkScaledImageCache::GetByteLimit();
 }
 
 size_t SkGraphics::SetImageCacheByteLimit(size_t newLimit) {
     return SkScaledImageCache::SetByteLimit(newLimit);
 }