Fix thread unsafe mutex initialization.

src/effects/gradients/SkGradientShader.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 "SkGradientShaderPriv.h"
 #include "SkLinearGradient.h"
 #include "SkRadialGradient.h"
@@ skipping 552 matching lines @@
     if (!fCache || fCache->getAlpha() != alpha) {
         fCache.reset(SkNEW_ARGS(GradientShaderCache, (alpha, *this)));
     }
     // Increment the ref counter inside the mutex to ensure the returned pointer is still valid.
     // Otherwise, the pointer may have been overwritten on a different thread before the object's
     // ref count was incremented.
     fCache.get()->ref();
     return fCache;
 }
 
+SK_DECLARE_STATIC_MUTEX(gGradientCacheMutex);
 /*
  *  Because our caller might rebuild the same (logically the same) gradient
  *  over and over, we'd like to return exactly the same "bitmap" if possible,
  *  allowing the client to utilize a cache of our bitmap (e.g. with a GPU).
  *  To do that, we maintain a private cache of built-bitmaps, based on our
  *  colors and positions. Note: we don't try to flatten the fMapper, so if one
  *  is present, we skip the cache for now.
  */
 void SkGradientShaderBase::getGradientTableBitmap(SkBitmap* bitmap) const {
     // our caller assumes no external alpha, so we ensure that our cache is
@@ skipping 15 matching lines @@
     if (fColorCount > 2) {
         for (int i = 1; i < fColorCount; i++) {
             *buffer++ = fRecs[i].fPos;
         }
     }
     *buffer++ = fGradFlags;
     SkASSERT(buffer - storage.get() == count);
 
     ///////////////////////////////////
 
-    SK_DECLARE_STATIC_MUTEX(gMutex);
     static SkBitmapCache* gCache;
     // each cache cost 1K of RAM, since each bitmap will be 1x256 at 32bpp
     static const int MAX_NUM_CACHED_GRADIENT_BITMAPS = 32;
-    SkAutoMutexAcquire ama(gMutex);
+    SkAutoMutexAcquire ama(gGradientCacheMutex);
 
     if (NULL == gCache) {
         gCache = SkNEW_ARGS(SkBitmapCache, (MAX_NUM_CACHED_GRADIENT_BITMAPS));
     }
     size_t size = count * sizeof(int32_t);
 
     if (!gCache->find(storage.get(), size, bitmap)) {
         // force our cahce32pixelref to be built
         (void)cache->getCache32();
         bitmap->setInfo(SkImageInfo::MakeN32Premul(kCache32Count, 1));
@@ skipping 525 matching lines @@
             (*stops)[i] = stop;
             stop = i < outColors - 1 ? stop + random->nextUScalar1() * (1.f - stop) : 1.f;
         }
     }
     *tm = static_cast<SkShader::TileMode>(random->nextULessThan(SkShader::kTileModeCount));
 
     return outColors;
 }
 
 #endif