Fix thread unsafe mutex initialization.

include/core/SkInstCnt.h

Index: include/core/SkInstCnt.h
diff --git a/include/core/SkInstCnt.h b/include/core/SkInstCnt.h
index 1839ee1dbdc6720d9c6b0870ea10e52dbe901c7a..a401071d80ad3804d4d5100952d94e4fed6d1638 100644
--- a/include/core/SkInstCnt.h
+++ b/include/core/SkInstCnt.h
@@ -73,10 +73,16 @@ extern bool gPrintInstCount;
             return gChildren;                                               \
         }                                                                   \
                                                                             \
+        static void create_mutex(SkMutex** mutex) {                         \
+            *mutex = SkNEW(SkMutex);                                        \
+        }                                                                   \
         static SkBaseMutex& GetChildrenMutex() {                            \
-            SK_DECLARE_STATIC_MUTEX(childrenMutex);                         \
-            return childrenMutex;                                           \
+            static SkMutex* childrenMutex = (SkMutex*)className::SkInstanceCountHelper::nil; \

[mtklein, 2014/07/25 12:35:33]

Just curious, how come static SkMutex* childrenMutex; is no good?  Or = NULL?

[bungeman-skia, 2014/07/25 14:40:40]

Because that would require an out of line definition (only static const
primitives are allowed to be defined in a class). We did a bunch of work before
to get away from the error prone two part declare and define of this instance
counting class, and I'd like to avoid it for just this. One would think to get
around this with intptr_t, but it would still have to be static const and the
compiler can ignore where it's used and use the class value directly.

+            SK_DECLARE_STATIC_ONCE(once);                                   \

[mtklein, 2014/07/25 12:35:33]

Can't we still use SK_DECLARE_STATIC_MUTEX to make the mutex a static member?

[bungeman-skia, 2014/07/25 14:40:40]

See above, it's the same situation as the pointer, requiring a top level
definition.

+            SkOnce(&once, create_mutex, &childrenMutex);                    \
+            return *childrenMutex;                                          \
         }                                                                   \
+        static const intptr_t nil = (intptr_t)NULL;                         \
                                                                             \
     } fInstanceCountHelper;                                                 \
                                                                             \