Upstream: Launch WebApkActivity from WebAPK.

chrome/android/java/AndroidManifest.xml

Index: chrome/android/java/AndroidManifest.xml
diff --git a/chrome/android/java/AndroidManifest.xml b/chrome/android/java/AndroidManifest.xml
index 858b3f3da8dc2df40f1ff8bec89a900d40868958..ee83c2cc7c459c3e1d4cd465e72317ae4f122bd2 100644
--- a/chrome/android/java/AndroidManifest.xml
+++ b/chrome/android/java/AndroidManifest.xml
@@ -382,6 +382,7 @@ by a child template that "extends" this file.
         <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"