Files.app: Clear the analytics ID every time the app starts.

BUG=461946

TBR=mtomasz

Review URL: https://codereview.chromium.org/961863004

Cr-Commit-Position: refs/heads/master@{#318301}

ui/file_manager/file_manager/background/js/background.js

@@ -627,8 +627,14 @@ FileBrowserBackground.prototype.initContextMenu_ = function() {
   });
 };
 
+// Ensure that the user gets a new analytics ID each time Files.app starts.
+// NOTE: This must be called before FileBrowserBackground is instantiated.
+// TODO(kenobi): Revisit this once users have the ability to do this themselves.
+metrics.clearUserId();
+
 /**
  * Singleton instance of Background.
+ * NOTE: This must come after the call to metrics.clearUserId.
  * @type {FileBrowserBackground}
  */
 window.background = new FileBrowserBackground();

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

@@ -70,3 +70,16 @@ metrics.umaEnabledFilter_ = function(hit) {
     hit.cancel();
   }
 };
+
+/**
+ * Clears the previously set analytics user id.
+ */
+metrics.clearUserId = function() {
+  chrome.storage.local.remove(
+     'google-analytics.analytics.user-id',
+     function () {
+       if (chrome.runtime.lastError) {
+         throw new Error(chrome.runtime.lastError.message);
+       }
+     });
+};