Extract some logic from transport_dib into shared_memory.

base/memory/shared_memory.h

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef BASE_MEMORY_SHARED_MEMORY_H_
 #define BASE_MEMORY_SHARED_MEMORY_H_
 
 #include "build/build_config.h"
 
 #include <string>
@@ skipping 112 matching lines @@
 
 #if defined(OS_POSIX)
   // The underlying OS primitives are duplicated.
   // |clean_up_resources_on_destruction| indicates whether the underlying OS
   // primitives are cleaned up on destruction.
   static SharedMemoryHandle DeepCopyHandle(
       const SharedMemoryHandle& handle,
       bool clean_up_resources_on_destruction);
 #endif
 
+#if defined(OS_POSIX) && !defined(OS_ANDROID)

[erikchen, 2015/05/30 00:00:35]

I find longer preprocessor conditionals easier to read than nested preprocessor
conditionals.

+  // Returns the size of the shared memory region referred to by |handle|.
+  // Returns '-1' on a failure to determine the size.
+  static int GetSizeFromSharedMemoryHandle(const SharedMemoryHandle& handle);
+#endif  // defined(OS_POSIX) && !defined(OS_ANDROID)
+
   // Creates a shared memory object as described by the options struct.
   // Returns true on success and false on failure.
   bool Create(const SharedMemoryCreateOptions& options);
 
   // Creates and maps an anonymous shared memory segment of size size.
   // Returns true on success and false on failure.
   bool CreateAndMapAnonymous(size_t size);
 
   // Creates an anonymous shared memory segment of size size.
   // Returns true on success and false on failure.
@@ skipping 188 matching lines @@
   }
 
  private:
   SharedMemory* shared_memory_;
   DISALLOW_COPY_AND_ASSIGN(SharedMemoryAutoLockDeprecated);
 };
 
 }  // namespace base
 
 #endif  // BASE_MEMORY_SHARED_MEMORY_H_