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/task_unittest.cc b/webrtc/base/task_unittest.cc
index b09373e..f3ccc24 100644
--- a/webrtc/base/task_unittest.cc
+++ b/webrtc/base/task_unittest.cc
@@ -33,7 +33,7 @@
 namespace rtc {
 
 static int64_t GetCurrentTime() {
-  return static_cast<int64_t>(Time()) * 10000;
+  return TimeMillis() * 10000;
 }
 
 // feel free to change these numbers.  Note that '0' won't work, though