Adds touch feedback to tray icons in touchview when --ash-enable-touchview-touch-feedback flag is passed.

TEST=WebNotificationTrayTest.MAYBE_NoTouchFeedback, WebNotificationTrayTest.MAYBE_MaximizeModeTouchFeedback, WebNotificationTrayTest.MAYBE_TouchFeedbackCancellation
BUG=398398

Review URL: https://codereview.chromium.org/515573002

Cr-Commit-Position: refs/heads/master@{#293608}
diff --git a/chrome/browser/about_flags.cc b/chrome/browser/about_flags.cc
index 8cc1c3c..1c9c9961 100644
--- a/chrome/browser/about_flags.cc
+++ b/chrome/browser/about_flags.cc
@@ -1028,13 +1028,20 @@
     kOsCrOS,
     SINGLE_VALUE_TYPE(ash::switches::kAshEnableTouchViewTesting),
   },
+  {
+    "ash-enable-touch-view-touch-feedback",
+    IDS_FLAGS_ASH_ENABLE_TOUCH_VIEW_TOUCH_FEEDBACK_NAME,
+    IDS_FLAGS_ASH_ENABLE_TOUCH_VIEW_TOUCH_FEEDBACK_DESCRIPTION,
+    kOsCrOS,
+    SINGLE_VALUE_TYPE(ash::switches::kAshEnableTouchViewTouchFeedback),
+  },
   { "ash-disable-text-filtering-in-overview-mode",
     IDS_FLAGS_ASH_DISABLE_TEXT_FILTERING_IN_OVERVIEW_MODE_NAME,
     IDS_FLAGS_ASH_DISABLE_TEXT_FILTERING_IN_OVERVIEW_MODE_DESCRIPTION,
     kOsCrOS,
     SINGLE_VALUE_TYPE(ash::switches::kAshDisableTextFilteringInOverviewMode),
   },
-#endif
+#endif  // defined(USE_ASH)
 #if defined(OS_CHROMEOS)
   {
     "enable-carrier-switching",