Adds extension APIs of events on changing volume.

chrome/browser/accessibility_events.cc

Index: chrome/browser/accessibility_events.cc
diff --git a/chrome/browser/accessibility_events.cc b/chrome/browser/accessibility_events.cc
index 79a1126e16e399dbd6bdc87eeb46f3de57492d72..04a10b0260c3c689cce6abc152ba55ac8f04e588 100644
--- a/chrome/browser/accessibility_events.cc
+++ b/chrome/browser/accessibility_events.cc
@@ -188,6 +188,24 @@ void AccessibilityListBoxInfo::SerializeToDict(DictionaryValue *dict) const {
   dict->SetInteger(keys::kItemCountKey, item_count_);
 }
 
+AccessibilityVolumeInfo::AccessibilityVolumeInfo(Profile* profile,
+                                                 double volume,
+                                                 bool is_mute)
+    : AccessibilityControlInfo(profile, "volume"),
+      volume_(volume),
+      is_mute_(is_mute) {
+}
+
+const char* AccessibilityVolumeInfo::type() const {
+  return keys::kTypeVolume;
+}
+
+void AccessibilityVolumeInfo::SerializeToDict(DictionaryValue *dict) const {
+  AccessibilityControlInfo::SerializeToDict(dict);
+  dict->SetDouble(keys::kVolumeKey, volume_);
+  dict->SetBoolean(keys::kIsVolumeMuteKey, is_mute_);
+}
+
 AccessibilityMenuInfo::AccessibilityMenuInfo(Profile* profile,
                                              const std::string& menu_name)
     : AccessibilityControlInfo(profile, menu_name) {