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

src/ports/SkThread_none.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 "SkThread.h"
@@ skipping 18 matching lines @@
 }
 void sk_membar_aquire__after_atomic_dec() { }
 
 int32_t sk_atomic_conditional_inc(int32_t* addr) {
     int32_t value = *addr;
     if (value != 0) ++*addr;
     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() {}
 
 SkMutex::~SkMutex() {}
 
 #ifndef SK_USE_POSIX_THREADS
 void SkMutex::acquire() {}
 void SkMutex::release() {}
 #endif
 
 //////////////////////////////////////////////////////////////////////////
 
 static void* gSpecific;
 
 void* SkTLS::PlatformGetSpecific(bool) {
     return gSpecific;
 }
 
 void SkTLS::PlatformSetSpecific(void* ptr) {
     gSpecific = ptr;
 }