Revert of Disabling NOTREACHED which we're hitting flakily in browser tests.

webrtc/modules/video_coding/codecs/vp9/vp9_frame_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 55 matching lines @@
     }
     // Otherwise create one.
     if (available_buffer == nullptr) {
       available_buffer = new rtc::RefCountedObject<Vp9FrameBuffer>();
       allocated_buffers_.push_back(available_buffer);
       if (allocated_buffers_.size() > max_num_buffers_) {
         LOG(LS_WARNING)
             << allocated_buffers_.size() << " Vp9FrameBuffers have been "
             << "allocated by a Vp9FrameBufferPool (exceeding what is "
             << "considered reasonable, " << max_num_buffers_ << ").";
-
-        // TODO(phoglund): this limit is being hit in tests since Oct 5 2016.
-        // See https://bugs.chromium.org/p/webrtc/issues/detail?id=6484.
-        // RTC_NOTREACHED();
+        RTC_NOTREACHED();
       }
     }
   }
 
   available_buffer->SetSize(min_size);
   return available_buffer;
 }
 
 int Vp9FrameBufferPool::GetNumBuffersInUse() const {
   int num_buffers_in_use = 0;
@@ skipping 40 matching lines @@
     buffer->Release();
     // When libvpx fails to decode and you continue to try to decode (and fail)
     // libvpx can for some reason try to release the same buffer multiple times.
     // Setting |priv| to null protects against trying to Release multiple times.
     fb->priv = nullptr;
   }
   return 0;
 }
 
 }  // namespace webrtc