make ntp apps promo work correctly

when the promo is showing, use the promo link even if the user clicks on the icon rather than the promo button. Additionally, fix the referrer for clicks on the promo button (by using launchApp).

BUG=82857
TEST=manual


Review URL: http://codereview.chromium.org/8767002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@112601 0039d316-1c4b-4281-b951-d872f2087c98

chrome/browser/resources/ntp4/apps_page.js

@@ -369,6 +369,7 @@ cr.define('ntp4', function() {
           this.appsPromoExtras_.querySelector('.apps-promo-heading');
       this.appsPromoLink_ =
           this.appsPromoExtras_.querySelector('.apps-promo-link');
+      this.appsPromoLink_.addEventListener('click', this.onClick_.bind(this));
 
       this.appsPromoLogo_ = this.ownerDocument.createElement('img');
       this.appsPromoLogo_.className = 'apps-promo-logo';
@@ -437,9 +438,7 @@ cr.define('ntp4', function() {
       var is_promo = this.appsPromoExtras_ &&
           window.getComputedStyle(this.appsPromoExtras_).display != 'none';
       var url = !this.appData_.is_webstore ? '' :
-          is_promo ? appendParam(this.appsPromoLink_.href,
-                                 'utm_source',
-                                 'chrome-ntp-promo') :
+          is_promo ? this.appsPromoLink_.href :
                      appendParam(this.appData_.url,
                                  'utm_source',
                                  'chrome-ntp-icon');