Fixed Ash.WindowSelector.TimeInOverview UMA metric reporting wrong time.

BUG=381703

Review URL: https://codereview.chromium.org/317393002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@275610 0039d316-1c4b-4281-b951-d872f2087c98

ash/wm/overview/window_selector.cc

@@ -95,6 +95,7 @@ WindowSelector::WindowSelector(const WindowList& windows,
       restore_focus_window_(aura::client::GetFocusClient(
           Shell::GetPrimaryRootWindow())->GetFocusedWindow()),
       ignore_activations_(false),
+      overview_start_time_(base::Time::Now()),
       selected_grid_index_(0) {
   DCHECK(delegate_);
   Shell* shell = Shell::GetInstance();