Fix performance issues in Google Sheets

- when firing an active descendant change event on a content editable, we were
  serializing line breaks which took approximately ~600MS. The line break
  calculation was not only slow, but wrong (got stuck and put repeated new lines
  at the same offset). Unfortunately, <textarea> still needs line break
  information, so keeping for the !richlyEditable but editable case.

- Sheets sends empty strings through the ChromeVox Classic speak api. This
  should never be allowed. It causes ChromeVox output to be flushed and stopped.

- value changes get fired on root web area. Root web areas usually have '' as
  their values. This also caused output to be prematurely cut off.

Cq-Include-Trybots: master.tryserver.chromium.linux:closure_compilation
Change-Id: Ide73784a23db7bc92aef51de917801dab439dbba
Reviewed-on: https://chromium-review.googlesource.com/964781Reviewed-by: Dominic Mazzoni <dmazzoni@chromium.org>
Commit-Queue: David Tseng <dtseng@chromium.org>
Cr-Commit-Position: refs/heads/master@{#543589}

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

@@ -283,6 +283,12 @@ cvox.ChromeVoxBackground.prototype.injectChromeVoxIntoTabs = function(tabs) {
  */
 cvox.ChromeVoxBackground.prototype.onTtsMessage = function(msg) {
   if (msg['action'] == 'speak') {
+    // The only caller sending this message is a ChromeVox Classic api client.
+    // Disallow empty strings.
+    if (msg['text'] == '') {
+      return;
+    }
+
     this.tts.speak(
         msg['text'],
         /** cvox.QueueMode */ msg['queueMode'], msg['properties']);

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

@@ -192,11 +192,6 @@ DesktopAutomationHandler.prototype = {
    * @param {!AutomationEvent} evt
    */
   onAriaAttributeChanged: function(evt) {
-    if (evt.target.activeDescendant) {
-      this.onActiveDescendantChanged(evt);
-      return;
-    }
-
     if (evt.target.state.editable)
       return;
     this.onEventIfInRange(evt);
@@ -306,8 +301,6 @@ DesktopAutomationHandler.prototype = {
           .withBraille(curRange, curRange, Output.EventType.NAVIGATE)
           .go();
     }
-
-    this.onActiveDescendantChanged(evt);
   },
 
   /**
@@ -434,6 +427,10 @@ DesktopAutomationHandler.prototype = {
    * @param {!AutomationEvent} evt
    */
   onValueChanged: function(evt) {
+    // Skip root web areas.
+    if (evt.target.role == RoleType.ROOT_WEB_AREA)
+      return;
+
     // Skip all unfocused text fields.
     if (!evt.target.state[StateType.FOCUSED] &&
         evt.target.state[StateType.EDITABLE])

content/renderer/accessibility/blink_ax_tree_source.cc

@@ -914,15 +914,17 @@ void BlinkAXTreeSource::SerializeNode(WebAXObject src,
 
 #if defined(OS_CHROMEOS)
       // This attribute will soon be deprecated; see crbug.com/669134.
-      WebVector<int> src_line_breaks;
-      src.LineBreaks(src_line_breaks);
-      if (src_line_breaks.size()) {
-        std::vector<int32_t> line_breaks;
-        line_breaks.reserve(src_line_breaks.size());
-        for (size_t i = 0; i < src_line_breaks.size(); ++i)
-          line_breaks.push_back(src_line_breaks[i]);
-        dst->AddIntListAttribute(ax::mojom::IntListAttribute::kLineBreaks,
-                                 line_breaks);
+      if (src.IsEditable() && !src.IsRichlyEditable()) {
+        WebVector<int> src_line_breaks;
+        src.LineBreaks(src_line_breaks);
+        if (src_line_breaks.size()) {
+          std::vector<int32_t> line_breaks;
+          line_breaks.reserve(src_line_breaks.size());
+          for (size_t i = 0; i < src_line_breaks.size(); ++i)
+            line_breaks.push_back(src_line_breaks[i]);
+          dst->AddIntListAttribute(ax::mojom::IntListAttribute::kLineBreaks,
+                                   line_breaks);
+        }
       }
 #endif  // defined OS_CHROMEOS
     }