Fix RateTracker to set an initial reference time when first updated.

BUG=4442
R=mflodman@webrtc.org, pbos@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/43829004

Cr-Commit-Position: refs/heads/master@{#8751}
git-svn-id: http://webrtc.googlecode.com/svn/trunk@8751 4adac7df-926f-26a2-2b94-8c16560cd09d

talk/media/base/videoengine_unittest.h

@@ -844,17 +844,6 @@ class VideoMediaChannelTest : public testing::Test,
         EXPECT_TRUE(WaitAndSendFrame(1000 / fps));
         EXPECT_FRAME_WAIT(frame + i * fps, codec.width, codec.height, kTimeout);
       }
-      cricket::VideoMediaInfo info;
-      EXPECT_TRUE(channel_->GetStats(&info));
-      // For webrtc, |framerate_sent| and |framerate_rcvd| depend on periodic
-      // callbacks (1 sec).
-      // Received |fraction_lost| and |packets_lost| are from sent RTCP packet.
-      // One sent packet needed (sent about once per second).
-      // |framerate_input|, |framerate_decoded| and |framerate_output| are using
-      // RateTracker. RateTracker needs to be called twice (with >1 second in
-      // b/w calls) before a framerate is calculated.
-      // Therefore insert frames (and call GetStats each sec) for a few seconds
-      // before testing stats.
     }
     rtc::scoped_ptr<const rtc::Buffer> p(GetRtpPacket(0));
     EXPECT_EQ(codec.id, GetPayloadType(p.get()));