Add ability to return moved value from FunctorMessageHandler, Optional.

webrtc/base/optional.h

 /*
  *  Copyright 2015 The WebRTC Project Authors. All rights reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
@@ skipping 221 matching lines @@
 
   // Dereference with a default value in case we don't have a value.
   const T& value_or(const T& default_val) const {
     // The no-op call prevents the compiler from generating optimized code that
     // reads value_ even if !has_value_, but only if FunctionThatDoesNothing is
     // not completely inlined; see its declaration.).
     return has_value_ ? *optional_internal::FunctionThatDoesNothing(&value_)
                       : default_val;
   }
 
+  // Dereference and move value.
+  T ConsumeValue() {
+    RTC_DCHECK(has_value_);
+    return std::move(value_);
+  }
+
   // Equality tests. Two Optionals are equal if they contain equivalent values,
   // or if they're both empty.
   friend bool operator==(const Optional& m1, const Optional& m2) {
     return m1.has_value_ && m2.has_value_ ? m1.value_ == m2.value_
                                           : m1.has_value_ == m2.has_value_;
   }
   friend bool operator==(const Optional& opt, const T& value) {
     return opt.has_value_ && opt.value_ == value;
   }
   friend bool operator==(const T& value, const Optional& opt) {
@@ skipping 34 matching lines @@
     // construct it, and the Optional destructor won't automatically destroy
     // it. Basically, this just allocates a properly sized and aligned block of
     // memory in which we can manually put a T with placement new.
     T value_;
   };
 };
 
 }  // namespace rtc
 
 #endif  // WEBRTC_BASE_OPTIONAL_H_