Add assertHeld() to SkMutex.

src/core/SkPaint.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 "SkPaint.h"
 #include "SkAnnotation.h"
 #include "SkAutoKern.h"
@@ skipping 1719 matching lines @@
 static SkMaskGamma* gLinearMaskGamma = NULL;
 static SkMaskGamma* gMaskGamma = NULL;
 static SkScalar gContrast = SK_ScalarMin;
 static SkScalar gPaintGamma = SK_ScalarMin;
 static SkScalar gDeviceGamma = SK_ScalarMin;
 /**
  * The caller must hold the gMaskGammaCacheMutex and continue to hold it until
  * the returned SkMaskGamma pointer is refed or forgotten.
  */
 static const SkMaskGamma& cachedMaskGamma(SkScalar contrast, SkScalar paintGamma, SkScalar deviceGamma) {
+    gMaskGammaCacheMutex.assertHeld();
     if (0 == contrast && SK_Scalar1 == paintGamma && SK_Scalar1 == deviceGamma) {
         if (NULL == gLinearMaskGamma) {
             gLinearMaskGamma = SkNEW(SkMaskGamma);
         }
         return *gLinearMaskGamma;
     }
     if (gContrast != contrast || gPaintGamma != paintGamma || gDeviceGamma != deviceGamma) {
         SkSafeUnref(gMaskGamma);
         gMaskGamma = SkNEW_ARGS(SkMaskGamma, (contrast, paintGamma, deviceGamma));
         gContrast = contrast;
@@ skipping 979 matching lines @@
     }
 #ifdef SK_BUILD_FOR_ANDROID
     if (dirty & kPaintOptionsAndroid_DirtyBit) {
         SkPaintOptionsAndroid options;
         options.unflatten(buffer);
         paint->setPaintOptionsAndroid(options);
     }
 #endif
     SkASSERT(dirty == paint->fDirtyBits);
 }