test_app: Add ControlledFrame feature flag to launch command line (#47)

Part of recent work separated Controlled Frame from the IWA
feature flag. Now, Controlled Frame has to be enabled separately
from IWAs.

test_app/README.md

@@ -52,15 +52,15 @@ python3 -m iwa_http_server.py
 2. Execute Chrome with the following flags once.
 
 ```sh
-$CHROME --enable-features=IsolatedWebApps,IsolatedWebAppDevMode
+$CHROME --enable-features=IsolatedWebApps,IsolatedWebAppDevMode,ControlledFrame
 ```
 
 **Optional:** Use the `--user-data-dir` flag to install the IWA in a separate
 Chrome profile. For example:
 
 ```sh
 $CHROME --user-data-dir=$HOME/tmp \
-        --enable-features=IsolatedWebApps,IsolatedWebAppDevMode
+        --enable-features=IsolatedWebApps,IsolatedWebAppDevMode,ControlledFrame
 ```
 
 The user data directory can be cleared to start Chrome in a fresh profile.