Add a 'unique' method to SkRefCnt, document the usage, and add support.

src/ports/SkThread_win.cpp

 
 /*
  * Copyright 2008 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 <windows.h>
@@ skipping 31 matching lines @@
         }
         if (_InterlockedCompareExchange(reinterpret_cast<LONG*>(addr),
                                         value + 1,
                                         value) == value) {
             return value;
         }
     }
 }
 void sk_membar_aquire__after_atomic_conditional_inc() { }
 
+int32_t sk_atomic_unprotected_read(const volatile int32_t & x) {
+    return x;
+}
+
 SkMutex::SkMutex() {
     SK_COMPILE_ASSERT(sizeof(fStorage) > sizeof(CRITICAL_SECTION),
                       NotEnoughSizeForCriticalSection);
     InitializeCriticalSection(reinterpret_cast<CRITICAL_SECTION*>(&fStorage));
 }
 
 SkMutex::~SkMutex() {
     DeleteCriticalSection(reinterpret_cast<CRITICAL_SECTION*>(&fStorage));
 }
 
@@ skipping 65 matching lines @@
 #pragma const_seg()
 
 #else
 
 #pragma data_seg(".CRT$XLB")
 PIMAGE_TLS_CALLBACK skia_tls_callback = onTLSCallback;
 #pragma data_seg()
 
 #endif
 }