Move DumpBacktrace() to checks.cc and cleanup both the code and the necessary platform checks.

src/platform-win32.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 873 matching lines @@
   // To avoid Visual Studio runtime support the following code can be used
   // instead
   // __asm { int 3 }
   __debugbreak();
 #else
   ::DebugBreak();
 #endif
 }
 
 
-void OS::DumpBacktrace() {
-  // Currently unsupported.
-}
-
-
 class Win32MemoryMappedFile : public OS::MemoryMappedFile {
  public:
   Win32MemoryMappedFile(HANDLE file,
                         HANDLE file_mapping,
                         void* memory,
                         int size)
       : file_(file),
         file_mapping_(file_mapping),
         memory_(memory),
         size_(size) { }
@@ skipping 536 matching lines @@
   ASSERT(result);
 }
 
 
 
 void Thread::YieldCPU() {
   Sleep(0);
 }
 
 } }  // namespace v8::internal