Improve UI for unpacked extensions failing to load

chrome/browser/resources/extensions/extension_code.js

+// Copyright 2014 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';
+
+  /**
+   * ExtensionCode is an element which displays code in a styled div, and is
+   * designed to highlight errors.
+   */
+  function ExtensionCode(div) {
+    div.__proto__ = ExtensionCode.prototype;
+    return div;
+  }
+
+  ExtensionCode.prototype = {
+    __proto__: HTMLDivElement.prototype,
+
+    /**
+     * Populate the content area of the code div with the given code. This will
+     * highlight the erroneous section (if any).
+     * @param {Object} code An object with four strings: beforeHighlight,
+     *     afterHighlight, highlight, and the message. The 'highlight' strings
+     *     represent the three portions of the file's content to display - the
+     *     portion which is most relevant and should be emphasized (highlight),
+     *     and the parts both before and after this portion. The message is the
+     *     error message, which will be the mouseover hint for the highlighted
+     *     region. These may be empty.
+     *  @param {string} emptyMessage The message to display if the code
+     *     object is empty (e.g., 'could not load code').
+     */
+    populate: function(code, emptyMessage) {
+      // Clear any remnant content, so we don't have multiple code listed.
+      this.clear();
+
+      var sourceDiv = document.createElement('div');
+      sourceDiv.classList.add('extension-code-source');
+      this.appendChild(sourceDiv);
+
+      // If there's no code, then display an appropriate message.
+      if (!code) {
+        var span = document.createElement('span');
+        span.textContent = emptyMessage;
+        sourceDiv.appendChild(span);
+        return;
+      }
+
+      var lineCount = 0;
+      var createSpan = function(source, isHighlighted) {
+        lineCount += source.split('\n').length - 1;
+        var span = document.createElement('span');
+        span.className = isHighlighted ? 'extension-code-highlighted-source' :
+                                         'extension-code-normal-source';
+        span.textContent = source;
+        return span;
+      };
+
+      if (code.beforeHighlight)
+        sourceDiv.appendChild(createSpan(code.beforeHighlight, false));
+
+      if (code.highlight) {
+        var highlightSpan = createSpan(code.highlight, true);
+        highlightSpan.title = code.message;
+        sourceDiv.appendChild(highlightSpan);
+      }
+
+      if (code.afterHighlight)
+        sourceDiv.appendChild(createSpan(code.afterHighlight, false));
+
+      // Make the line numbers. This should be the number of line breaks + 1
+      // (the last line doesn't break, but should still be numbered).
+      var content = '';
+      for (var i = 1; i < lineCount + 1; ++i)
+        content += i + '\n';
+      var span = document.createElement('span');
+      span.textContent = content;
+
+      var linesDiv = document.createElement('div');
+      linesDiv.classList.add('extension-code-line-numbers');
+      linesDiv.appendChild(span);
+      this.insertBefore(linesDiv, this.firstChild);
+    },
+
+    /**
+     * Clears the content of the element.
+     */
+    clear: function() {
+      while (this.firstChild)
+        this.removeChild(this.firstChild);
+    },
+
+    /**
+     * Scrolls to the error, if there is one. This cannot be called when the
+     * div is hidden.
+     */
+    scrollToError: function() {
+      var errorSpan = this.querySelector('.extension-code-highlighted-source');
+      if (errorSpan)
+        errorSpan.scrollIntoView(false);  // Scroll to bottom of view.
+    }
+  };
+
+  // Export
+  return {
+    ExtensionCode: ExtensionCode
+  };
+});