NetEq jitter calculation now done in uint64_t.

The timestamps are 32 bit and can (conceivably) be spaced far enough
apart for the calculation, which is done in Q4, to overflow.

BUG=chromium:653268

Review-Url: https://codereview.webrtc.org/2460393002
Cr-Commit-Position: refs/heads/master@{#14856}
diff --git a/webrtc/modules/audio_coding/neteq/rtcp.h b/webrtc/modules/audio_coding/neteq/rtcp.h
index eacb328..d222cea 100644
--- a/webrtc/modules/audio_coding/neteq/rtcp.h
+++ b/webrtc/modules/audio_coding/neteq/rtcp.h
@@ -48,7 +48,7 @@
                                      // report was generated.
   uint32_t expected_prior_;  // Expected number of packets, at the time of the
                              // last report.
-  uint32_t jitter_;  // Current jitter value.
+  int64_t jitter_;  // Current jitter value in Q4.
   int32_t transit_;  // Clock difference for previous packet.
 
   RTC_DISALLOW_COPY_AND_ASSIGN(Rtcp);