Linux native notifications: Fix clickable buttons

On Peter's notification generator [1], creating a notification with
"Action" set to alert() and everyting else set to default settings,
notification->clickable() is false when I expected the notification to
be clickable.  This CL always makes notifications clickable regardless
of the clickable() state.

[1] https://tests.peter.sh/notification-generator/

BUG=676220
R=peter@chromium.org
CC=thestig@chromium.org

Change-Id: I326b6fa5b64e8a18aa95ea47dfbcbe5caaaa9bdc
Reviewed-on: https://chromium-review.googlesource.com/748213Reviewed-by: Peter Beverloo <peter@chromium.org>
Commit-Queue: Thomas Anderson <thomasanderson@chromium.org>
Cr-Commit-Position: refs/heads/master@{#513159}

chrome/browser/notifications/notification_platform_bridge_linux.cc

@@ -622,12 +622,10 @@ class NotificationPlatformBridgeLinuxImpl
         actions.push_back(id);
         actions.push_back(label);
       }
-      if (notification->clickable()) {
-        // Special case: the pair ("default", "") will not add a button,
-        // but instead makes the entire notification clickable.
-        actions.push_back(kDefaultButtonId);
-        actions.push_back("");
-      }
+      // Special case: the id "default" will not add a button, but
+      // instead makes the entire notification clickable.
+      actions.push_back(kDefaultButtonId);
+      actions.push_back("Activate");
       // Always add a settings button for web notifications.
       if (notification_type != NotificationCommon::EXTENSION) {
         actions.push_back(kSettingsButtonId);