Change default timestamp to 64 bits in all webrtc directories.

BUG=
R=pbos@webrtc.org, pthatcher@webrtc.org, solenberg@webrtc.org

Review URL: https://codereview.webrtc.org/1835053002 .

Cr-Commit-Position: refs/heads/master@{#12646}
diff --git a/webrtc/base/logging.h b/webrtc/base/logging.h
index 886b5d8..802dfa7 100644
--- a/webrtc/base/logging.h
+++ b/webrtc/base/logging.h
@@ -156,7 +156,7 @@
   // If this is not called externally, the LogMessage ctor also calls it, in
   // which case the logging start time will be the time of the first LogMessage
   // instance is created.
-  static uint32_t LogStartTime();
+  static int64_t LogStartTime();
 
   // Returns the wall clock equivalent of |LogStartTime|, in seconds from the
   // epoch.