Unified: Set tooltip for Notifications count or dnd icon.

This change updates tooltip for the latest design spec.
The tooltips describe either the number of notifications or being in
DnD mode, so that these should work well for a11y label as well.

Bug: 888072
Change-Id: Ifed382eca722c6948cf14a9f834ad0bb314c1629
Reviewed-on: https://chromium-review.googlesource.com/c/1306935Reviewed-by: Tetsui Ohkubo <tetsui@chromium.org>
Commit-Queue: Tatsuhisa Yamaguchi <yamaguchi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#603784}

ash/ash_strings.grd

@@ -276,6 +276,14 @@ This file contains the strings for ash.
       <message name="IDS_ASH_STATUS_TRAY_CAST_STOP" desc="The label used in the tray popup to stop casting.">
         Stop
       </message>
+      <message name="IDS_ASH_STATUS_TRAY_QUIET_MODE_TOOLTIP" desc="The tooltip text for the status area icon to tell do-not-disturb mode is currently on.">
+        Do Not Disturb is on
+      </message>
+      <message name="IDS_ASH_STATUS_TRAY_NOTIFICATIONS_COUNT_TOOLTIP" desc="The tooltip text for a status area icon to describe number of notifications. [ICU Syntax]">
+        {NUM_NOTIFICATIONS, plural,
+         =1 {1 notification}
+         other {# notifications}}
+      </message>
 
       <message name="IDS_ASH_STATUS_TRAY_BLUETOOTH" desc="The label used as the header in the bluetooth popup.">
         Bluetooth

ash/system/unified/notification_counter_view.cc

@@ -92,8 +92,6 @@ class NumberIconImageSource : public gfx::CanvasImageSource {
 NotificationCounterView::NotificationCounterView(Shelf* shelf)
     : TrayItemView(shelf) {
   CreateImageView();
-  image_view()->set_tooltip_text(
-      l10n_util::GetStringUTF16(IDS_ASH_STATUS_TRAY_NOTIFICATIONS_LABEL));
   SetVisible(false);
   Shell::Get()->session_controller()->AddObserver(this);
 }
@@ -116,6 +114,8 @@ void NotificationCounterView::Update() {
         gfx::CanvasImageSource::MakeImageSkia<NumberIconImageSource>(icon_id));
     count_for_display_ = icon_id;
   }
+  image_view()->set_tooltip_text(l10n_util::GetPluralStringFUTF16(
+      IDS_ASH_STATUS_TRAY_NOTIFICATIONS_COUNT_TOOLTIP, notification_count));
   SetVisible(true);
 }
 
@@ -126,6 +126,8 @@ void NotificationCounterView::OnSessionStateChanged(
 
 QuietModeView::QuietModeView(Shelf* shelf) : TrayItemView(shelf) {
   CreateImageView();
+  image_view()->set_tooltip_text(
+      l10n_util::GetStringUTF16(IDS_ASH_STATUS_TRAY_QUIET_MODE_TOOLTIP));
   SetVisible(false);
   Shell::Get()->session_controller()->AddObserver(this);
 }