[Android FRE] Make talkback more helpful for FRE dialog

This CL:
Makes the lightweight/non-lightweight first run dialog
- be announced as "Chrome First Run Experience" by Talkback
- be listed as "Chrome First Run Experience" in Android Recents
on Android-Pre-L

BUG=766844

Change-Id: Id5567400dc6dbcc467cb773d3e7a4037860537f7
Reviewed-on: https://chromium-review.googlesource.com/775857Reviewed-by: Ted Choc <tedchoc@chromium.org>
Commit-Queue: Peter Kotwicz <pkotwicz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#517819}

chrome/android/java/AndroidManifest.xml

@@ -461,6 +461,7 @@ by a child template that "extends" this file.
         <activity android:name="org.chromium.chrome.browser.firstrun.FirstRunActivity"
             android:theme="@style/FirstRunTheme"
             {% block first_run_activity_common %}
+            android:label="@string/fre_activity_label"
             android:launchMode="singleInstance"
             android:excludeFromRecents="true"
             android:autoRemoveFromRecents="true"

chrome/android/java/strings/android_chrome_strings.grd

@@ -2187,6 +2187,9 @@ To obtain new licenses, connect to the internet and play your downloaded content
       </message>
 
       <!-- First Run strings -->
+      <message name="IDS_FRE_ACTIVITY_LABEL" desc="Label for first run dialog in Android Recents.">
+        Chrome First Run Experience
+      </message>
       <message name="IDS_FRE_SKIP_TEXT" desc="Text for second page skip button">
         No thanks
       </message>