Bug 1256615 - Partially restore removed <activity-alias>. r=sebastian

Bug 1242213 removed the entire <activity-alias>.  Sadly, users who
added the Firefox icon to their dock (for example, Samsung's Touchwiz
dock) will see the icon disappear when they upgrade, because the
intent filter disappears.  (That is, the icon is connected to .App and
action MAIN, not to the package and action MAIN.)

This patch restores the .App <activity-alias> for action MAIN.  It
doesn't add the launcher and other categories, which could lead to
multiple launcher icons.  New users that add the Firefox icon to their
dock will use .BrowserApp, but sadly we'll need to maintain this alias
essentially forever to support existing dock icons.

MozReview-Commit-ID: 1o9XS5MEs1s

--HG--
extra : rebase_source : 8f4e1321da475bf2dcfca88c5807bf26c940b1c5
extra : amend_source : 3429ff0eaec0edb02e5e47678252bf5a2de74d3f

mobile/android/base/AndroidManifest.xml.in

@@ -141,6 +141,18 @@
             </intent-filter>
         </activity>
 
+        <!-- Bug 1256615: We published a .App alias and we need to maintain it
+             forever.  If we don't, dock icons (e.g., Samsung Touchwiz icons)
+             will disappear because the intent filter details change. -->
+        <activity-alias android:name=".App"
+                        android:label="@MOZ_APP_DISPLAYNAME@"
+                        android:targetActivity="@MOZ_ANDROID_BROWSER_INTENT_CLASS@">
+            <intent-filter>
+                <action android:name="android.intent.action.MAIN" />
+                <category android:name="android.intent.category.DEFAULT" />
+            </intent-filter>
+        </activity-alias>
+
         <service android:name="org.mozilla.gecko.GeckoService" />
 
         <activity android:name="org.mozilla.gecko.trackingprotection.TrackingProtectionPrompt"