Files.app: Switch analytics to use the chrome version, not the app version, for tracking.

The files.app version in the manifest is not regularly updated.  We'll get more accurate version info by using the chrome major release version.

BUG=469258

Review URL: https://codereview.chromium.org/1035483004

Cr-Commit-Position: refs/heads/master@{#322106}

ui/file_manager/file_manager/common/js/metrics.js

@@ -50,7 +50,12 @@ metrics.getTracker = function() {
  * @private
  */
 metrics.createTracker_ = function() {
-  metrics.analytics_ = analytics.getService('Files app');
+  var chromeVersion = /Chrome\/([0-9]*)\.[0-9.]*/.exec(navigator.userAgent);
+  if (chromeVersion && chromeVersion[1]) {
+    metrics.analytics_ = analytics.getService('Files app', chromeVersion[1]);
+  } else {
+    metrics.analytics_ = analytics.getService('Files app', '0.0');
+  }
 
   // Create a tracker, add a filter that only enables analytics when UMA is
   // enabled.