Add an about:flag to control WebApk enablement.

chrome/app/generated_resources.grd

Index: chrome/app/generated_resources.grd
diff --git a/chrome/app/generated_resources.grd b/chrome/app/generated_resources.grd
index 517261bee52d62b16aeb6229c87a977c8909510a..ec06a0df6fa344eee2c5a7eb729e3a50767d795a 100644
--- a/chrome/app/generated_resources.grd
+++ b/chrome/app/generated_resources.grd
@@ -15065,6 +15065,14 @@ Please check your email at <ph name="ACCOUNT_EMAIL">$2<ex>jane.doe@gmail.com</ex
       <message name="IDS_FLAGS_TAB_SWITCHER_IN_DOCUMENT_MODE_DESCRIPTION" desc="Description for the flag to enable tab switcher in document mode.">
         If enabled, a tab switcher will show even when 'merge tabs and apps' option is on in the settings.
       </message>
+        
+      <!-- WebApks -->
+      <message name="IDS_FLAGS_ENABLE_WEBAPK" desc="Name for the flag to enable WebApk feature.">
+        Enable WebApks

[pkotwicz, 2016/08/15 15:27:52]

Nit ⬆️case. "Enable WebApks" -> "Enable WebAPKs"

[Yaron, 2016/08/16 01:08:42]

Done.

+      </message>
+      <message name="IDS_FLAGS_ENABLE_WEBAPK_DESCRIPTION" desc="Description for the flag to enable WebApk feature.">
+        Enables packaging PWAs into an Android WebApk. Requires sending data to a chrome server to generate the application.

[pkotwicz, 2016/08/15 15:27:52]

"WebApk" -> "WebAPK"

[Yaron, 2016/08/16 01:08:42]

Done.

+      </message>
     </if>
 
     <message name="IDS_FLAGS_ENABLE_BROTLI_NAME" desc="Title for the flag to enable Brotli Content-Encoding.">