Upstream: Launch WebApkActivity from WebAPK.

chrome/android/java/AndroidManifest.xml

 <?xml version="1.0" encoding="utf-8"?>
 <!-- Copyright 2015 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. -->
 
 <!--
 Note: This is a jinja2 template, processed at build time into the final manifest.
 
 Blocks denoted with { % block some_name % }foo{ % endblock % } can be overridden
 by a child template that "extends" this file.
@@ skipping 364 matching lines @@
                 <action android:name="com.google.android.apps.chrome.webapps.WebappManager.ACTION_START_WEBAPP" />
                 <category android:name="android.intent.category.DEFAULT" />
             </intent-filter>
         </activity>
         <activity-alias android:name="com.google.android.apps.chrome.webapps.WebappManager"
             android:targetActivity="org.chromium.chrome.browser.webapps.WebappLauncherActivity">
         </activity-alias>
         <activity android:name="org.chromium.chrome.browser.webapps.WebappActivity"
             android:theme="@style/WebappTheme"
             android:label="@string/webapp_activity_title"
+            android:launchMode="singleTop"

[gone, 2016/05/21 00:07:28]

Why would this change to singleTop?  Won't that prevent having more than one
non-WebAPK web app listed in Recents on L+?  If this is important, have you
considered subclassing WebappActivity?

[Xi Han, 2016/05/25 14:37:58]

Your concern is right. We have that change because on L, the application icon in
Android recents is the icon of the host activity. When the WebappActivity is
started as a new task, the icon of a WebApk will be Chrome's icon since
WebappActivity is Chrome's activity. So we have to prevent staring
WebAppActivity as a new task on the stack, but a singleTop task hosting by
WebAPK's MainActivity. 
I Introduce WebApkActivity and move related logic to there. For the long run, it
benefits as keeping the current behavior of WebappActivity.

             android:documentLaunchMode="intoExisting"
             android:windowSoftInputMode="adjustResize"
             android:persistableMode="persistNever"
             android:hardwareAccelerated="false"
             android:configChanges="orientation|keyboardHidden|keyboard|screenSize|mcc|mnc|screenLayout|smallestScreenSize">
         </activity>
         <activity-alias android:name="com.google.android.apps.chrome.webapps.WebappActivity"
             android:targetActivity="org.chromium.chrome.browser.webapps.WebappActivity"
             android:label="@string/webapp_activity_title">
         </activity-alias>
@@ skipping 405 matching lines @@
              choose the first MediaRouteController that can play it, so the order of the list can be important.
              The most specific MediaRouteControllers should be listed first, followed by more generic ones.
              The downstream manifest replaces this block, and hence replaces the list of media route
              controllers with its own list. -->
         <meta-data android:name="org.chromium.content.browser.REMOTE_MEDIA_PLAYERS"
             android:value="org.chromium.chrome.browser.media.remote.DefaultMediaRouteController"/>
 
         {% endblock %}
     </application>
 </manifest>