Removing more noise from user action sequencer.

Launcher_ClickOnAppListButton is generated both on launcher start and closing. Replaced (in sequencer) with Launcher_Show (new) and Launcher_Dismiss (see prev CL) pair.

Bug=712331

Review-Url: https://codereview.chromium.org/2854283005
Cr-Commit-Position: refs/heads/master@{#469477}

tools/metrics/actions/actions.xml

@@ -8804,7 +8804,7 @@ should be able to be added at any place in this file.
   <description>Please enter the description of this user action.</description>
 </action>
 
-<action name="Launcher_ClickOnApplistButton">
+<action name="Launcher_ClickOnApplistButton" not_user_triggered="true">
   <owner>Please list the metric's owners. Add more owner tags as needed.</owner>
   <description>Please enter the description of this user action.</description>
 </action>
@@ -8831,6 +8831,11 @@ should be able to be added at any place in this file.
   </description>
 </action>
 
+<action name="Launcher_Show">
+  <owner>vadimt@chromium.org</owner>
+  <description>Launcher got shown.</description>
+</action>
+
 <action name="Launcher_SwitchTask">
   <owner>bruthig@google.com</owner>
   <owner>tdanderson@google.com</owner>

ui/app_list/presenter/app_list_presenter_impl.cc

@@ -75,6 +75,7 @@ void AppListPresenterImpl::Show(int64_t display_id) {
     SetView(view);
   }
   presenter_delegate_->OnShown(display_id);
+  base::RecordAction(base::UserMetricsAction("Launcher_Show"));
 }
 
 void AppListPresenterImpl::Dismiss() {