Fix editable text selection

We need to special-case setting selections when the focused node is itself editable.
- make no adjustments for the selected node; placing selection outside of the editable content causes key presses to go to the page
- if we are trying to select the entire node, set the selection index to 0 (placing selection at the beginning of the node); otherwise, use the character offset

TEST=move to a text field or content editable via ChromeVox commands; verify typing works to echo the keys. Furthermore, verify that in a content editable with headings, links, etc, jump commands move the selection. Finally, verify ChromeVox text movement commands (e.g. next character), moves selection in single line editables.
BUG=656349,658045
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:closure_compilation

Review-Url: https://codereview.chromium.org/2442503008
Cr-Commit-Position: refs/heads/master@{#427106}

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

@@ -166,6 +166,10 @@ cursors.Cursor.prototype = {
     if (!adjustedNode)
       return null;
 
+    // Make no adjustments if we're within editable content.
+    if (adjustedNode.state.editable)
+      return adjustedNode;
+
     // Selections over line break nodes are broken.
     var parent = adjustedNode.parent;
     var grandparent = parent && parent.parent;
@@ -197,8 +201,13 @@ cursors.Cursor.prototype = {
   get selectionIndex_() {
     var adjustedIndex = this.index_;
 
-    // Selecting things under a line break is currently broken.
-    if (this.node.role == RoleType.inlineTextBox &&
+    if (!this.node)
+      return -1;
+
+    if (this.node.state.editable) {
+      return this.index_ == cursors.NODE_INDEX ? 0 : this.index_;
+    } else if (this.node.role == RoleType.inlineTextBox &&
+    // Selections under a line break are broken.
         this.node.parent && this.node.parent.role != RoleType.lineBreak) {
       if (adjustedIndex == cursors.NODE_INDEX)
         adjustedIndex = 0;