[Mac] Make initial visibility of the promote button on the about page

deterministic.

An uninitialized member variable was at fault.

R=thakis@chromium.org

Review URL: https://codereview.chromium.org/131933003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@244260 0039d316-1c4b-4281-b951-d872f2087c98

chrome/browser/ui/webui/help/version_updater_mac.mm

@@ -57,8 +57,9 @@ VersionUpdater* VersionUpdater::Create() {
   return new VersionUpdaterMac;
 }
 
-VersionUpdaterMac::VersionUpdaterMac() {
-  keystone_observer_.reset([[KeystoneObserver alloc] initWithUpdater:this]);
+VersionUpdaterMac::VersionUpdaterMac()
+    : show_promote_button_(false),
+      keystone_observer_([[KeystoneObserver alloc] initWithUpdater:this]) {
 }
 
 VersionUpdaterMac::~VersionUpdaterMac() {