Move SetTargetSendBitrates logic from default module to payload router.

This cl just moves the logic form the default module
SetTargetSendBitrates to PayloadRouter. There might be glitch / mismatch
in size between trate the vector and rtp modules. This was the same in
the default module and is quite hard to protect from before we have the
new video API.

I also removed some test form rtp_rtcp_impl_unittest that were affected
by this change. The test tests code that isn't implemented, hence the
DISABLED_, and this will never be implemented in the RTP module, rather
the payload router in the future.

BUG=769
R=pbos@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/42419004

Cr-Commit-Position: refs/heads/master@{#8453}
git-svn-id: http://webrtc.googlecode.com/svn/trunk@8453 4adac7df-926f-26a2-2b94-8c16560cd09d

webrtc/modules/rtp_rtcp/source/rtp_rtcp_impl.h

@@ -288,8 +288,7 @@ class ModuleRtpRtcpImpl : public RtpRtcp {
   // Send a request for a keyframe.
   virtual int32_t RequestKeyFrame() OVERRIDE;
 
-  virtual void SetTargetSendBitrate(
-      const std::vector<uint32_t>& stream_bitrates) OVERRIDE;
+  virtual void SetTargetSendBitrate(uint32_t bitrate_bps) OVERRIDE;
 
   virtual int32_t SetGenericFECStatus(bool enable,
                                       uint8_t payload_type_red,