[MD Extensions] Include the manifest code snippet in load errors

chrome/browser/resources/md_extensions/code_section.js

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 cr.define('extensions', function() {
   'use strict';
 
   var CodeSection = Polymer({
     is: 'extensions-code-section',
 
     properties: {
       /**
        * The code this object is displaying.
        * @type {?chrome.developerPrivate.RequestFileSourceResponse}
        */
       code: {
         type: Object,
         // We initialize to null so that Polymer sees it as defined and calls
         // isMainHidden_().
         value: null,
       },
 
       /**
        * The string to display if no code is set.
        * @type {string}
        */
       noCodeError: String,

[michaelpg, 2017/03/24 02:59:01]

I might just be silly, but I'm not sure which of these "noCodeError" means:

* "error: no code!" (an error we've encountered that says we couldn't show the
code for some unexpected reason), or
* "no, not a code error!" (a boolean saying whether or not there is a code error
to show the extension developer), or
* "message for a non-code-based error" (a string to show when the developer's
extension has an error that doesn't come from their code, i.e. when it's a load
error)

I suspect it's the last one, so a more accurate string would be
"errorTextToShowWhenTheErrorThisUIIsForIsNotInTheCode" but pithier. But then I'd
wonder if a <code-section> element is the right choice for a generic error --
one that doesn't involve a section of code.

Feel free to swing by my desk tmrw if what I just said makes no sense. It's been
a long day...

[Devlin, 2017/03/24 16:03:08]

It's actually the first - we fail to load the relevant source file.  Renamed to
couldNotDisplayCode and clarified in the comment.

Even for load errors, it's usually a 'code' error.  e.g. if an extension
manifest is invalid json (like missing a comma or an end quote), the error is
"manifest is invalid json, line 10, column 3, syntax error", and we'll load up
the manifest and display it, highlighting the error spot.  The only time we
*don't* load a file is if, for instance, the error is that the file itself is
missing (like not having a manifest.json file), in which case we show "Could not
load manifest.json".

     },
 
     /**
      * Computes the content of the line numbers span, which basically just
      * contains 1\n2\n3\n... for the number of lines.
      * @return {string}
      * @private
      */
     computeLineNumbersContent_: function() {
       if (!this.code)
         return '';
 
       var lines = [this.code.beforeHighlight,
                    this.code.highlight,
                    this.code.afterHighlight].join('').match(/\n/g);
       var lineCount = lines ? lines.length : 0;
       var textContent = '';
       for (var i = 1; i <= lineCount; ++i)
         textContent += i + '\n';
       return textContent;
     },
 
     /**
+     * Returns true if no code could be displayed.

[michaelpg, 2017/03/24 02:59:01]

As above, I'm asking myself *why* the code couldn't be displayed.

[Devlin, 2017/03/24 16:03:08]

added "e.g. because the file could not be loaded."

      * @return {boolean}
-     * @private
      */
-    isMainHidden_: function() {
-      return !this.code;
+    isEmpty: function() {

[michaelpg, 2017/03/24 02:59:01]

nit: move above @private method

[Devlin, 2017/03/24 16:03:08]

Done.

+      return !this.code ||
+             (!this.code.beforeHighlight && !this.code.highlight &&
+              !this.code.afterHighlight);
     },
   });
 
   return {CodeSection: CodeSection};
 });