Add perf histogram and tests for inline signin

chrome/browser/resources/gaia_auth/main.js

Index: chrome/browser/resources/gaia_auth/main.js
diff --git a/chrome/browser/resources/gaia_auth/main.js b/chrome/browser/resources/gaia_auth/main.js
index 936ea1d13f8daaf301efae5bd0cf9abb40b5f463..8efa28cc995b4f30c417e5f0fdbb0fd5bc191d1f 100644
--- a/chrome/browser/resources/gaia_auth/main.js
+++ b/chrome/browser/resources/gaia_auth/main.js
@@ -61,6 +61,7 @@ Authenticator.prototype = {
     this.initialFrameUrl_ = params.frameUrl || this.constructInitialFrameUrl_();
     this.initialFrameUrlWithoutParams_ = stripParams(this.initialFrameUrl_);
     this.loaded_ = false;
+    this.load_start_ts_ = 0;
 
     document.addEventListener('DOMContentLoaded', this.onPageLoad.bind(this));
     document.addEventListener('enableSAML', this.onEnableSAML_.bind(this));
@@ -168,6 +169,8 @@ Authenticator.prototype = {
     var gaiaFrame = $('gaia-frame');
     gaiaFrame.partition = this.partitionId_;
     gaiaFrame.src = this.initialFrameUrl_;
+    this.load_start_ts_ = Date.now();
+
     if (this.inlineMode_) {
       gaiaFrame.addEventListener(
           'loadstop', this.onWebviewLoadstop_.bind(this, gaiaFrame));
@@ -260,7 +263,9 @@ Authenticator.prototype = {
 
   onLoginUILoaded: function() {
     var msg = {
-      'method': 'loginUILoaded'
+      'method': 'loginUILoaded',
+      'load_start_ts': this.load_start_ts_,
+      'load_stop_ts': Date.now()
     };
     window.parent.postMessage(msg, this.parentPage_);
     if (this.inlineMode_) {