Fix thread unsafe mutex initialization.

include/core/SkInstCnt.h

 /*
  * Copyright 2012 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 
 #ifndef SkInstCnt_DEFINED
 #define SkInstCnt_DEFINED
@@ skipping 55 matching lines @@
         static int32_t* GetInstanceCountPtr() {                             \
             static int32_t gInstanceCount;                                  \
             return &gInstanceCount;                                         \
         }                                                                   \
                                                                             \
         static SkTArray<int (*)(int, bool)>*& GetChildren() {               \
             static SkTArray<int (*)(int, bool)>* gChildren;                 \
             return gChildren;                                               \
         }                                                                   \
                                                                             \
+        static void create_mutex(SkMutex** mutex) {                         \
+            *mutex = SkNEW(SkMutex);                                        \
+        }                                                                   \
         static SkBaseMutex& GetChildrenMutex() {                            \
-            SK_DECLARE_STATIC_MUTEX(childrenMutex);                         \
-            return childrenMutex;                                           \
+            static SkMutex* childrenMutex;                                  \
+            SK_DECLARE_STATIC_ONCE(once);                                   \
+            SkOnce(&once, className::SkInstanceCountHelper::create_mutex, &childrenMutex);\
+            return *childrenMutex;                                          \

[bungeman-skia, 2014/07/25 15:44:07]

Making this body look like

SK_DECLARE_STATIC_LAZY_PTR(SkMutex, childrenMutex);
return *childrenMutex.get();

seems like it would work even better, but this file is in include/core and
SkLazyPtr.h is in src/core, which might not be on the search path. I think that
would make the include something like #include "../../src/core/SkLazyPtr.h"
which requires that 'src' and 'include' be next to each other.

         }                                                                   \
                                                                             \
     } fInstanceCountHelper;                                                 \
                                                                             \
     static int32_t GetInstanceCount() {                                     \
         return *SkInstanceCountHelper::GetInstanceCountPtr();               \
     }                                                                       \
                                                                             \
     static void exitPrint() {                                               \
         CheckInstanceCount(0, true);                                        \
@@ skipping 44 matching lines @@
 #define SK_DECLARE_INST_COUNT(className) static void AddInstChild() { INHERITED::AddInstChild(); }
 #define SK_DECLARE_INST_COUNT_ROOT(className) static void AddInstChild() { }
 #endif
 
 // Following are deprecated. They are defined only for backwards API compatibility.
 #define SK_DECLARE_INST_COUNT_TEMPLATE(className) SK_DECLARE_INST_COUNT(className)
 #define SK_DEFINE_INST_COUNT(className)
 #define SK_DEFINE_INST_COUNT_TEMPLATE(templateInfo, className)
 
 #endif // SkInstCnt_DEFINED