Add simple path navigation to chrome://discards.

While I'm in there add a style to make the swimlane dividers impossible
to select, which was a persistent nuisance.

Bug: 1068233
Change-Id: Ie4b1b10fe39823102e9ec36d6396865b49e5de32
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2144261
Commit-Queue: Sigurður Ásgeirsson <siggi@chromium.org>
Reviewed-by: dpapad <dpapad@chromium.org>
Cr-Commit-Position: refs/heads/master@{#758021}

chrome/browser/resources/discards/discards_main.html

@@ -22,6 +22,7 @@
         overflow: hidden;
       }
     </style>
+    <iron-location path="{{path}}"></iron-location>
     <cr-tabs selected="{{selected}}" tab-names="[[tabs]]"></cr-tabs>
 
     <iron-pages selected="[[selected]]">

chrome/browser/resources/discards/discards_main.js

@@ -4,6 +4,7 @@
 
 import 'chrome://resources/cr_elements/hidden_style_css.m.js';
 import 'chrome://resources/cr_elements/cr_tabs/cr_tabs.m.js';
+import 'chrome://resources/polymer/v3_0/iron-location/iron-location.js';
 import 'chrome://resources/polymer/v3_0/iron-pages/iron-pages.js';
 import './database_tab.js';
 import './discards_tab.js';
@@ -21,6 +22,13 @@ Polymer({
     selected: {
       type: Number,
       value: 0,
+      observer: 'selectedChanged_',
+    },
+
+    path: {
+      type: String,
+      value: '',
+      observer: 'pathChanged_',
     },
 
     tabs: {
@@ -28,4 +36,38 @@ Polymer({
       value: () => ['Discards', 'Database', 'Graph'],
     },
   },
+
+  /**
+   * Updates the location hash on selection change.
+   * @param {number} newValue
+   * @param {number|undefined} oldValue
+   * @private
+   */
+  selectedChanged_(newValue, oldValue) {
+    if (oldValue != undefined) {
+      this.path = '/' + this.tabs[newValue].toLowerCase();
+    }
+  },
+
+  /**
+   * Returns the index of the currently selected tab corresponding to the
+   * path or zero if no match.
+   * @param {string} path
+   * @return {number}
+   * @private
+   */
+  selectedFromPath_(path) {
+    const index = this.tabs.findIndex(tab => path === tab.toLowerCase());
+    return Math.max(index, 0);
+  },
+
+  /**
+   * Updates the selection property on path change.
+   * @param {string} newValue
+   * @param {string|undefined} oldValue
+   * @private
+   */
+  pathChanged_(newValue, oldValue) {
+    this.selected = this.selectedFromPath_(newValue.substr(1));
+  },
 });

chrome/browser/resources/discards/graph_doc_template.html

@@ -34,6 +34,7 @@ URL. As result, this document needs to be self-contained, hence inline scripts.
 
       .separator {
         font: italic 13px sans-serif;
+        user-select: none;
       }
     </style>
   <script src="https://ajax.googleapis.com/ajax/libs/d3js/5.7.0/d3.min.js"