Enable -Winconsistent-missing-override flag.

webrtc/common_video/i420_buffer_pool.cc

 /*
  *  Copyright (c) 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 12 matching lines @@
 
  private:
   ~PooledI420Buffer() override {}
 
   int width() const override { return buffer_->width(); }
   int height() const override { return buffer_->height(); }
   const uint8_t* DataY() const override { return buffer_->DataY(); }
   const uint8_t* DataU() const override { return buffer_->DataU(); }
   const uint8_t* DataV() const override { return buffer_->DataV(); }
 
-  bool IsMutable() { return HasOneRef(); }
+  bool IsMutable() override { return HasOneRef(); }
   // Make the IsMutable() check here instead of in |buffer_|, because the pool
   // also has a reference to |buffer_|.
   uint8_t* MutableDataY() override {
     RTC_DCHECK(IsMutable());
     return const_cast<uint8_t*>(buffer_->DataY());
   }
   uint8_t* MutableDataU() override {
     RTC_DCHECK(IsMutable());
     return const_cast<uint8_t*>(buffer_->DataU());
   }
@@ skipping 52 matching lines @@
   // Allocate new buffer.
   rtc::scoped_refptr<I420Buffer> buffer = new rtc::RefCountedObject<I420Buffer>(
       width, height);
   if (zero_initialize_)
     buffer->InitializeData();
   buffers_.push_back(buffer);
   return new rtc::RefCountedObject<PooledI420Buffer>(buffers_.back());
 }
 
 }  // namespace webrtc