Prevent repeated output

In some instances, we receive a significant number of attribute changes within a short delay.

This change throws away attribute changes that generate the same output on the same target.

Test: manually on settings page. Verify that ChromeVox only announces the radio button once rather than > 30 times (and plays the radio button earcon 30 times).
Change-Id: I92127ad074b3a73ce269077cae6b69ba71f59c52
Reviewed-on: https://chromium-review.googlesource.com/1211972
Commit-Queue: David Tseng <dtseng@chromium.org>
Reviewed-by: Dominic Mazzoni <dmazzoni@chromium.org>
Cr-Commit-Position: refs/heads/master@{#589700}

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

@@ -293,8 +293,16 @@ Background.prototype = {
     for (var prop in opt_speechProps)
       o.format('!' + prop);
 
-    if (!skipOutput)
+    if (!skipOutput) {
       o.go();
+
+      if (range.start.node) {
+        // Update the DesktopAutomationHandler's state as well to ensure event
+        // handlers don't repeat this output.
+        DesktopAutomationHandler.instance.updateLastAttributeState(
+            range.start.node, o);
+      }
+    }
   },
 
   /**

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

@@ -48,6 +48,12 @@ DesktopAutomationHandler = function(node) {
   /** @private {AutomationNode} */
   this.lastValueTarget_ = null;
 
+  /** @private {AutomationNode} */
+  this.lastAttributeTarget_;
+
+  /** @private {Output} */
+  this.lastAttributeOutput_;
+
   /** @private {string} */
   this.lastRootUrl_ = '';
 
@@ -151,6 +157,11 @@ DesktopAutomationHandler.prototype = {
     output.withRichSpeechAndBraille(
         ChromeVoxState.instance.currentRange, prevRange, evt.type);
     output.go();
+
+    // Update some state here to ensure attribute changes don't duplicate
+    // output.
+    this.lastAttributeTarget_ = evt.target;
+    this.lastAttributeOutput_ = output;
   },
 
   /**
@@ -166,12 +177,17 @@ DesktopAutomationHandler.prototype = {
 
     if (prev.contentEquals(cursors.Range.fromNode(evt.target)) ||
         evt.target.state.focused) {
-      // Intentionally skip setting range.
-      new Output()
-          .withRichSpeechAndBraille(
-              cursors.Range.fromNode(evt.target), prev,
-              Output.EventType.NAVIGATE)
-          .go();
+      var prevTarget = this.lastAttributeTarget_;
+      this.lastAttributeTarget_ = evt.target;
+      var prevOutput = this.lastAttributeOutput_;
+      this.lastAttributeOutput_ = new Output().withRichSpeechAndBraille(
+          cursors.Range.fromNode(evt.target), prev, Output.EventType.NAVIGATE);
+
+      if (evt.target == prevTarget && prevOutput &&
+          prevOutput.equals(this.lastAttributeOutput_))
+        return;
+
+      this.lastAttributeOutput_.go();
     }
   },
 
@@ -466,6 +482,17 @@ DesktopAutomationHandler.prototype = {
     this.shouldIgnoreDocumentSelectionFromAction_ = val;
   },
 
+  /**
+   * Update the state for the last attribute change that occurred in ChromeVox
+   * output.
+   * @param {!AutomationNode} node
+   * @param {!Output} output
+   */
+  updateLastAttributeState: function(node, output) {
+    this.lastAttributeTarget_ = node;
+    this.lastAttributeOutput_ = output;
+  },
+
   /**
    * Provides all feedback once a change event in a text field fires.
    * @param {!AutomationEvent} evt

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

@@ -1050,6 +1050,27 @@ Output.prototype = {
       chrome.accessibilityPrivate.setFocusRing(this.locations_);
   },
 
+  /**
+   * @return {boolean} True if this object is equal to |rhs|.
+   */
+  equals: function(rhs) {
+    if (this.speechBuffer_.length != rhs.speechBuffer_.length ||
+        this.brailleBuffer_.length != rhs.brailleBuffer_.length)
+      return false;
+
+    for (var i = 0; i < this.speechBuffer_.length; i++) {
+      if (this.speechBuffer_[i].toString() != rhs.speechBuffer_[i].toString())
+        return false;
+    }
+
+    for (var j = 0; j < this.brailleBuffer_.length; j++) {
+      if (this.brailleBuffer_[j].toString() != rhs.brailleBuffer_[j].toString())
+        return false;
+    }
+
+    return true;
+  },
+
   /**
    * Renders the given range using optional context previous range and event
    * type.