Mojo: Make mojo::Handle::value() return a reference instead of a value.

mojo/public/cpp/system/handle.h

 // Copyright 2014 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 MOJO_PUBLIC_CPP_SYSTEM_HANDLE_H_
 #define MOJO_PUBLIC_CPP_SYSTEM_HANDLE_H_
 
 #include <assert.h>
 #include <limits>
 
@@ skipping 156 matching lines @@
   void swap(Handle& other) {
     MojoHandle temp = value_;
     value_ = other.value_;
     other.value_ = temp;
   }
 
   bool is_valid() const {
     return value_ != kInvalidHandleValue;
   }
 
-  MojoHandle value() const { return value_; }
+  const MojoHandle& value() const { return value_; }
   MojoHandle* mutable_value() { return &value_; }
   void set_value(MojoHandle value) { value_ = value; }
 
  private:
   MojoHandle value_;
 
   // Copying and assignment allowed.
 };
 
 // Should have zero overhead.
@@ skipping 50 matching lines @@
 
 // Strict weak ordering, so that |Handle|s can be used as keys in |std::map|s,
 // etc.
 inline bool operator<(const Handle& a, const Handle& b) {
   return a.value() < b.value();
 }
 
 }  // namespace mojo
 
 #endif  // MOJO_PUBLIC_CPP_SYSTEM_HANDLE_H_