Added SharedMemory::MapFrom.

base/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_SHARED_MEMORY_H_
 #define BASE_SHARED_MEMORY_H_
 
 #include "build/build_config.h"
 
 #include <string>
@@ skipping 126 matching lines @@
 
   // Opens a shared memory segment based on a name.
   // If read_only is true, opens for read-only access.
   // Returns true on success, false on failure.
   bool Open(const std::string& name, bool read_only);
 
   // Maps the shared memory into the caller's address space.
   // Returns true on success, false otherwise.  The memory address
   // is accessed via the memory() accessor.  The mapped address is guaranteed to
   // have an alignment of at least MAP_MINIMUM_ALIGNMENT.
-  bool Map(size_t bytes);
+  bool Map(size_t bytes) {
+    return MapAt(0, bytes);
+  }
+
+  // Same as above, but with |offset| to specify from begining of the shared
+  // memory block to map.
+  // |offset| must be alignent to value of |SysInfo::VMAllocationGranularity()|.
+  bool MapAt(off_t offset, size_t bytes);
   enum { MAP_MINIMUM_ALIGNMENT = 32 };
 
   // Unmaps the shared memory from the caller's address space.
   // Returns true if successful; returns false on error or if the
   // memory is not mapped.
   bool Unmap();
 
   // Get the size of the shared memory backing file.
   // Note:  This size is only available to the creator of the
   // shared memory, and not to those that opened shared memory
@@ skipping 108 matching lines @@
   }
 
  private:
   SharedMemory* shared_memory_;
   DISALLOW_COPY_AND_ASSIGN(SharedMemoryAutoLock);
 };
 
 }  // namespace base
 
 #endif  // BASE_SHARED_MEMORY_H_