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

src/platform-cygwin.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 23 matching lines @@
 #include <stdarg.h>
 #include <strings.h>    // index
 #include <sys/time.h>
 #include <sys/mman.h>   // mmap & munmap
 #include <unistd.h>     // sysconf
 
 #undef MAP_TYPE
 
 #include "v8.h"
 
-#include "platform-posix.h"
 #include "platform.h"
 #include "simulator.h"
 #include "v8threads.h"
 #include "vm-state-inl.h"
 #include "win32-headers.h"
 
 namespace v8 {
 namespace internal {
 
 
@@ skipping 26 matching lines @@
   void* mbase = mmap(NULL, msize, prot, MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
   if (mbase == MAP_FAILED) {
     LOG(Isolate::Current(), StringEvent("OS::Allocate", "mmap failed"));
     return NULL;
   }
   *allocated = msize;
   return mbase;
 }
 
 
-void OS::DumpBacktrace() {
-  // Currently unsupported.
-}
-
-
 class PosixMemoryMappedFile : public OS::MemoryMappedFile {
  public:
   PosixMemoryMappedFile(FILE* file, void* memory, int size)
     : file_(file), memory_(memory), size_(size) { }
   virtual ~PosixMemoryMappedFile();
   virtual void* memory() { return memory_; }
   virtual int size() { return size_; }
  private:
   FILE* file_;
   void* memory_;
@@ skipping 248 matching lines @@
   return VirtualFree(base, 0, MEM_RELEASE) != 0;
 }
 
 
 bool VirtualMemory::HasLazyCommits() {
   // TODO(alph): implement for the platform.
   return false;
 }
 
 } }  // namespace v8::internal