Hangout remote desktop part II - background.html and AppLauncher

This CL:
- Moves background.js to background.html
- Introduces remoting.appLauncher that allows the caller to launch and close the webapp without knowing the implementation difference between a v1 app and a v2 app.

NOTRY=true
[email protected]

Review URL: https://codereview.chromium.org/450383003

Cr-Commit-Position: refs/heads/master@{#289096}
git-svn-id: svn://svn.chromium.org/chrome/trunk/src@289096 0039d316-1c4b-4281-b951-d872f2087c98
diff --git a/remoting/remoting_webapp.gypi b/remoting/remoting_webapp.gypi
index ea498b65..19692d1 100644
--- a/remoting/remoting_webapp.gypi
+++ b/remoting/remoting_webapp.gypi
@@ -11,6 +11,7 @@
     'generated_html_files': [
       '<(SHARED_INTERMEDIATE_DIR)/main.html',
       '<(SHARED_INTERMEDIATE_DIR)/wcs_sandbox.html',
+      '<(SHARED_INTERMEDIATE_DIR)/background.html',
     ],
   },
   'dependencies': [