Enhance ChromeVox selection

- backward selections were previously not implemented/supported. Add that feature in this change.
- suppress hints during selection.

chromevox_tests --gtest_filter=BackgroundTest.Selection

Test: manually select forwards and backwards in all possible granularities.
Bug: 854872
Change-Id: Ic26a9e2d1426e8fcea31323c33c42c3476b1bc4c
Reviewed-on: https://chromium-review.googlesource.com/1115913Reviewed-by: Dominic Mazzoni <dmazzoni@chromium.org>
Commit-Queue: David Tseng <dtseng@chromium.org>
Cr-Commit-Position: refs/heads/master@{#570865}

chrome/browser/resources/chromeos/chromevox/cvox2/background/background.js

@@ -230,16 +230,8 @@ Background.prototype = {
     var msg;
 
     if (this.pageSel_ && this.pageSel_.isValid() && range.isValid()) {
-      // Compute the direction of the endpoints of each range.
-
-      // Casts are ok because isValid checks node start and end nodes are
-      // non-null; Closure just doesn't eval enough to see it.
-      var startDir = AutomationUtil.getDirection(
-          this.pageSel_.start.node,
-          /** @type {!AutomationNode} */ (range.start.node));
-      var endDir = AutomationUtil.getDirection(
-          this.pageSel_.end.node,
-          /** @type {!AutomationNode} */ (range.end.node));
+      // Suppress hints.
+      o.withoutHints();
 
       // Selection across roots isn't supported.
       var pageRootStart = this.pageSel_.start.node.root;
@@ -248,21 +240,32 @@ Background.prototype = {
       var curRootEnd = range.end.node.root;
 
       // Disallow crossing over the start of the page selection and roots.
-      if (startDir == Dir.BACKWARD || pageRootStart != pageRootEnd ||
-          pageRootStart != curRootStart || pageRootEnd != curRootEnd) {
+      if (pageRootStart != pageRootEnd || pageRootStart != curRootStart ||
+          pageRootEnd != curRootEnd) {
         o.format('@end_selection');
         this.pageSel_ = null;
       } else {
         // Expand or shrink requires different feedback.
-        if (endDir == Dir.FORWARD &&
-            (this.pageSel_.end.node != range.end.node ||
-             this.pageSel_.end.index <= range.end.index)) {
+
+        // Page sel is the only place in ChromeVox where we used directed
+        // selections. It is important to keep track of the directedness in
+        // places, but when comparing to other ranges, take the undirected
+        // range.
+        var dir = this.pageSel_.normalize().compare(range);
+
+        if (dir) {
+          // Directed expansion.
           msg = '@selected';
         } else {
+          // Directed shrink.
           msg = '@unselected';
           selectedRange = prevRange;
         }
-        this.pageSel_ = new cursors.Range(this.pageSel_.start, range.end);
+        var wasBackwardSel =
+            this.pageSel_.start.compare(this.pageSel_.end) == Dir.BACKWARD ||
+            dir == Dir.BACKWARD;
+        this.pageSel_ = new cursors.Range(
+            this.pageSel_.start, wasBackwardSel ? range.start : range.end);
         if (this.pageSel_)
           this.pageSel_.select();
       }

chrome/browser/resources/chromeos/chromevox/cvox2/background/cursors.js

@@ -779,8 +779,13 @@ cursors.Range.prototype = {
    * Select the text contained within this range.
    */
   select: function() {
-    var startNode = this.start.selectionNode_;
-    var endNode = this.end.selectionNode_;
+    var start = this.start_, end = this.end_;
+    if (this.start.compare(this.end) == Dir.BACKWARD) {
+      start = this.end;
+      end = this.start;
+    }
+    var startNode = start.selectionNode_;
+    var endNode = end.selectionNode_;
 
     if (!startNode || !endNode)
       return;
@@ -790,10 +795,10 @@ cursors.Range.prototype = {
         startNode.root == endNode.root) {
       // We want to adjust to select the entire node for node offsets;
       // otherwise, use the plain character offset.
-      var startIndex = this.start.selectionIndex_;
-      var endIndex = this.end.index_ == cursors.NODE_INDEX ?
-          this.end.selectionIndex_ + 1 :
-          this.end.selectionIndex_;
+      var startIndex = start.selectionIndex_;
+      var endIndex = end.index_ == cursors.NODE_INDEX ?
+          end.selectionIndex_ + 1 :
+          end.selectionIndex_;
 
       // Richly editables should always set a caret, but not select. This makes
       // it possible to navigate through content editables using ChromeVox keys
@@ -827,6 +832,33 @@ cursors.Range.prototype = {
    */
   isValid: function() {
     return this.start.isValid() && this.end.isValid();
+  },
+
+  /**
+   * Compares this range with |rhs|.
+   * @param {cursors.Range} rhs
+   * @return {Dir|undefined} Dir.BACKWARD if |rhs| comes before this range in
+   * document order. Dir.FORWARD if |rhs| comes after this range. Undefined
+   * otherwise.
+   */
+  compare: function(rhs) {
+    var startDir = this.start.compare(rhs.start);
+    var endDir = this.end.compare(rhs.end);
+    if (startDir != endDir)
+      return undefined;
+
+    return startDir;
+  },
+
+  /**
+   * Returns an undirected version of this range.
+   * @return {!cursors.Range}
+   */
+  normalize: function() {
+    if (this.start.compare(this.end) == Dir.BACKWARD) {
+      return new cursors.Range(this.end, this.start);
+    }
+    return this;
   }
 };