Adds extension APIs of events on changing volume.

chrome/browser/extensions/extension_accessibility_api_constants.h

Index: chrome/browser/extensions/extension_accessibility_api_constants.h
diff --git a/chrome/browser/extensions/extension_accessibility_api_constants.h b/chrome/browser/extensions/extension_accessibility_api_constants.h
index ce02a7e34b579785ed4ae73ea26e69a6642fa2e6..fc1df5ac454af1b7a97c80914e00136d7895a37e 100644
--- a/chrome/browser/extensions/extension_accessibility_api_constants.h
+++ b/chrome/browser/extensions/extension_accessibility_api_constants.h
@@ -22,6 +22,8 @@ extern const char kSelectionStartKey[];
 extern const char kSelectionEndKey[];
 extern const char kCheckedKey[];
 extern const char kHasSubmenuKey[];
+extern const char kVolumeKey[];
+extern const char kIsVolumeMutedKey[];
 
 // Events.
 extern const char kOnWindowOpened[];
@@ -31,6 +33,7 @@ extern const char kOnControlAction[];
 extern const char kOnTextChanged[];
 extern const char kOnMenuOpened[];
 extern const char kOnMenuClosed[];
+extern const char kOnVolumeChanged[];
 
 // Types of controls that can receive accessibility events
 extern const char kTypeButton[];
@@ -43,6 +46,7 @@ extern const char kTypeMenuItem[];
 extern const char kTypeRadioButton[];
 extern const char kTypeTab[];
 extern const char kTypeTextBox[];
+extern const char kTypeVolume[];
 extern const char kTypeWindow[];
 
 };  // namespace extension_accessibility_api_constants