Changing the bitrate clamping in BitrateControllerImpl

This CL implements an alternative to the bitrate clamping that is done
in BitrateControllerImpl. The default behavior is unchanged, but if
the new algorithm is enabled the behavior is as follows:
When the new bitrate is lower than the sum of min bitrates, the
algorithm will give each observer up to its min bitrate, one
observer at a time, until the bitrate budget is depleted. Thus,
with this change, some observers may get less than their min bitrate,
or even zero.

Unit tests are implemented.

Also fixing two old lint warnings in the affected files.

This change is related to the auto-muter feature.

BUG=2436
R=stefan@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/2439005

git-svn-id: http://webrtc.googlecode.com/svn/trunk@5007 4adac7df-926f-26a2-2b94-8c16560cd09d

webrtc/video_engine/vie_channel_group.cc

@@ -108,7 +108,7 @@ class WrappingBitrateEstimator : public RemoteBitrateEstimator {
 ChannelGroup::ChannelGroup(ProcessThread* process_thread,
                            const Config& config)
     : remb_(new VieRemb()),
-      bitrate_controller_(BitrateController::CreateBitrateController()),
+      bitrate_controller_(BitrateController::CreateBitrateController(true)),
       call_stats_(new CallStats()),
       remote_bitrate_estimator_(new WrappingBitrateEstimator(remb_.get(),
                                 Clock::GetRealTimeClock(), process_thread)),