metrics: Collect full timestamps.

Update metrics.README.md and add a metrics_version field.

Bug: None
Change-Id: I17d9032bd787af2a6fc49f80d59e05152d5223b7
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/1406256
Reviewed-by: Andy Perelson <ajp@chromium.org>
Reviewed-by: Edward Lesmes <ehmaldonado@chromium.org>
Commit-Queue: Edward Lesmes <ehmaldonado@chromium.org>
diff --git a/metrics.py b/metrics.py
index 00d6e6d..937dbcd 100644
--- a/metrics.py
+++ b/metrics.py
@@ -198,6 +198,7 @@
         return func(*args, **kwargs)
 
     self._collecting_metrics = True
+    self.add('metrics_version', metrics_utils.CURRENT_VERSION)
     self.add('command', command_name)
     try:
       start = time.time()
@@ -213,7 +214,7 @@
     self.add('exit_code', exit_code)
 
     # Add metrics regarding environment information.
-    self.add('timestamp', metrics_utils.seconds_to_weeks(time.time()))
+    self.add('timestamp', time.time())
     self.add('python_version', metrics_utils.get_python_version())
     self.add('host_os', gclient_utils.GetMacWinOrLinux())
     self.add('host_arch', detect_host_arch.HostArch())