Stubbed runtime and app.runtime in caterpillar.js. Resolves #8.

src/js/caterpillar.js

 // Copyright 2015 Google Inc. All Rights Reserved.
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
 // You may obtain a copy of the License at
 //
 //     http://www.apache.org/licenses/LICENSE-2.0
 //
 // Unless required by applicable law or agreed to in writing, software
 // distributed under the License is distributed on an "AS IS" BASIS,
 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
 /**
  * Common utilities and types for Caterpillar.
  *
  * Must be included before any Caterpillar polyfills.
  */
 
 'use strict';
 
 // Set up a namespace if one doesn't already exist.
 if (!('chrome' in self))
   self.chrome = {};
 
 if (!chrome.caterpillar)
   chrome.caterpillar = {};
 
+// We need the chrome.runtime namespace to store errors in.
+if (!chrome.runtime)
+  chrome.runtime = { lastError: null };
+
+// Stub out chrome.app.runtime.onLaunched.addListener, since this always appears
+// in Chrome Apps.

[raymes, 2016/01/31 23:44:37]

I'm not sure what this comment means? Why is it stubbed out? Is it unsupported? 

[Matthew Alger, 2016/02/01 00:14:33]

chrome.app.runtime.onLaunched.addListener is used in the boilerplate of every
Chrome App to launch the main window. The fact we're moving the app from the
Chrome Apps platform to the web means this line is never necessary (unless you
are using multiple windows, which we don't support anyway). We don't support the
listener itself, so it needs to be stubbed out, or the service worker (which
imports all background scripts) will break (as undefined has no property
onLaunched).

[raymes, 2016/02/01 00:18:44]

Could you make the comment say something like this? I don't think it's
necessarily intuitive.

[Matthew Alger, 2016/02/01 00:36:52]

Done.

+if (!chrome.app)

[Matthew Alger, 2016/01/28 04:51:41]

Note that Chrome exports chrome.app, so we can't just check if chrome.app exists
and only stub then.

[raymes, 2016/01/31 23:44:37]

Could we just always override onLaunched? (do we really have to check whether it
exists?)

[Matthew Alger, 2016/02/01 00:14:33]

It's not obvious to me that Chrome doesn't/won't export chrome.app.runtime, and
if it does, we don't want to override that.

[raymes, 2016/02/01 00:18:44]

Why not override it? :) I think we had a similar discussion previously about
chrome.runtime?

[Matthew Alger, 2016/02/01 00:36:52]

Hmmm, okay. Done.

(Though if a chrome.app.runtime polyfill gets written, this would need to
change)

+  chrome.app = {};
+if (!chrome.app.runtime)
+  chrome.app.runtime = {};
+if (!chrome.app.runtime.onLaunched) {
+  chrome.app.runtime.onLaunched = {
+    addListener: function() {},
+  };
+}

[raymes, 2016/01/31 23:44:37]

Why did this code need to be moved?

[Matthew Alger, 2016/02/01 00:14:33]

- It's static, so I think it should go in a static file.
- This is common JS code for Caterpillar, so it should go in the common
Caterpillar JS file.
- It doesn't make sense to have this in caterpillar.py, since it isn't really
related to service worker generation.

[raymes, 2016/02/01 00:18:44]

Sounds good - this would be useful context to have in the CL description.

[Matthew Alger, 2016/02/01 00:36:52]

Done.

+
 (function() {
 
 /**
  * Sets an error message in lastError if chrome.runtime is loaded.

[raymes, 2016/02/01 00:18:44]

nit: this is no longer accurate, nor the @throws below.

[Matthew Alger, 2016/02/01 00:36:52]

! Done.

  *
  * @param {string} message The error message to set.
  *
  * @throws Error with given message if runtime is not loaded, and a warning that
  *     runtime isn't loaded.
  */
 chrome.caterpillar.setError = function(message) {
-  if (!chrome.runtime) {
-    console.warn('chrome.runtime not found; runtime errors may not be caught.');
-    throw new Error(message);
-  }
+  console.warn('Error set in lastError:', message);

[raymes, 2016/01/31 23:44:37]

Do we need to log warnings every time?

[Matthew Alger, 2016/02/01 00:14:33]

Hmm, I'm not sure. I don't think it really matters either way - do you have an
opinion on this?

[raymes, 2016/02/01 00:18:44]

I think removing it is ok.

[Matthew Alger, 2016/02/01 00:36:52]

Done.

   chrome.runtime.lastError = { 'message': message };
 };
 
-}).call(this);
+}).call(this);