IPH - Added triggers for Download page

components/feature_engagement_tracker/public/android/java/src/org/chromium/components/feature_engagement_tracker/EventConstants.java

+// Copyright 2017 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+package org.chromium.components.feature_engagement_tracker;
+
+/**
+ * EventConstants contains the String name of all in-product help events.

[David Trainor- moved to gerrit, 2017/04/17 23:03:41]

Should these be mirrored in native as well?  I can add that if you want, I need
them there.

[shaktisahu, 2017/04/19 02:39:11]

Ok. I didn't think they are needed in native. Yea, go ahead if you are adding
them there.

+ */
+public final class EventConstants {
+    public static final String USER_HAS_SEEN_DINO = "user_has_seen_dino";
+    public static final String DOWNLOAD_PAGE_STARTED = "download_page_started";
+
+    /**
+     * Do not instantiate.
+     */
+    private EventConstants() {}
+}