Add ChromeVox panel and implement caption display functionality.

chrome/browser/resources/chromeos/chromevox/braille/braille_display_manager.js

Index: chrome/browser/resources/chromeos/chromevox/braille/braille_display_manager.js
diff --git a/chrome/browser/resources/chromeos/chromevox/braille/braille_display_manager.js b/chrome/browser/resources/chromeos/chromevox/braille/braille_display_manager.js
index b94ef8674f5d2caf998d5930b55f05b39858492e..7e2762d9030180a8224e8711e7cf5309e86233f5 100644
--- a/chrome/browser/resources/chromeos/chromevox/braille/braille_display_manager.js
+++ b/chrome/browser/resources/chromeos/chromevox/braille/braille_display_manager.js
@@ -195,11 +195,12 @@ cvox.BrailleDisplayManager.prototype.refresh_ = function() {
   if (this.realDisplayState_.available) {
     chrome.brailleDisplayPrivate.writeDots(buf);
   }
+
+  var start = this.brailleToTextPosition_(viewPort.start);
+  var end = this.brailleToTextPosition_(viewPort.end);
+  var brailleText = this.content_.text.toString().substring(start, end);
   if (cvox.BrailleCaptionsBackground.isEnabled()) {
-    var start = this.brailleToTextPosition_(viewPort.start);
-    var end = this.brailleToTextPosition_(viewPort.end);
-    cvox.BrailleCaptionsBackground.setContent(
-        this.content_.text.toString().substring(start, end), buf);
+    cvox.BrailleCaptionsBackground.setContent(brailleText, buf);
   }
 };