Add annotations to SkSharedMutex.

src/core/SkSharedMutex.h

 /*
  * Copyright 2015 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef SkSharedLock_DEFINED
 #define SkSharedLock_DEFINED
 
 #include "SkAtomics.h"
 #include "SkSemaphore.h"
 #include "SkTypes.h"
-
+    
 // This is a shared lock implementation similar to pthreads rwlocks. This implementation is
 // cribbed from Preshing's article:
 // http://preshing.com/20150316/semaphores-are-surprisingly-versatile/
 //
 // This lock does not obey strict queue ordering. It will always alternate between readers and
 // a single writer.
 class SkSharedMutex {
 public:
     SkSharedMutex();
-
+    ~SkSharedMutex();
     // Acquire lock for exclusive use.
     void acquire();
 
     // Release lock for exclusive use.
     void release();
 
     // Acquire lock for shared use.
     void acquireShared();
 
     // Release lock for shared use.
     void releaseShared();
 
 private:
     SkAtomic<int32_t> fQueueCounts;
     SkSemaphore fSharedQueue;
     SkSemaphore fExclusiveQueue;
 };
 
 #endif // SkSharedLock_DEFINED