Fixes Chrome find feedback in ChromeVox

R=dmazzoni@chromium.org

Fixed: 1068665
AX-Relnotes: Fixes Chrome find in page feedback in ChromeVox.
Change-Id: I00a434feb43da30ced04f01c63980ad568bf0233
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2213238
Commit-Queue: David Tseng <dtseng@chromium.org>
Reviewed-by: Dominic Mazzoni <dmazzoni@chromium.org>
Cr-Commit-Position: refs/heads/master@{#771353}

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

@@ -38,10 +38,33 @@ FindHandler.onTextMatch_ = function(evt) {
     return;
   }
 
+  // When a user types, a flurry of events gets sent from the tree updates being
+  // applied. Drop all but the first. Note that when hitting enter, there's only
+  // one marker changed ever sent.
+  const delta = new Date() - FindHandler.lastFindMarkerReceived;
+  FindHandler.lastFindMarkerReceived = new Date();
+  if (delta < FindHandler.DROP_MATCH_WITHIN_TIME_MS) {
+    return;
+  }
+
   const range = cursors.Range.fromNode(evt.target);
   ChromeVoxState.instance.setCurrentRange(range);
   new Output()
       .withRichSpeechAndBraille(range, null, Output.EventType.NAVIGATE)
       .go();
 };
+
+/**
+ * The amount of time where a subsequent find text marker is dropped from
+ * output.
+ * @const {number}
+ */
+FindHandler.DROP_MATCH_WITHIN_TIME_MS = 50;
+
+/**
+ * The last time a find marker was received.
+ * @type {!Date}
+ */
+FindHandler.lastFindMarkerReceived = new Date();
+
 });  // goog.scope