Add a new GetInstance() method for remaining files with singleton classes under chrome/browser.

chrome/browser/chromeos/usb_mount_observer.cc

Index: chrome/browser/chromeos/usb_mount_observer.cc
diff --git a/chrome/browser/chromeos/usb_mount_observer.cc b/chrome/browser/chromeos/usb_mount_observer.cc
index 2f1e7a413756abcffba3a5552ab9f8bd72ea301c..39461a2d63a6718611c19e3fa17e81e24a2dc3f5 100644
--- a/chrome/browser/chromeos/usb_mount_observer.cc
+++ b/chrome/browser/chromeos/usb_mount_observer.cc
@@ -23,6 +23,11 @@ const int kPopupTop = 0;
 const int kPopupWidth = 250;
 const int kPopupHeight = 300;
 
+// static
+USBMountObserver* USBMountObserver::Get() {
+  return Singleton<USBMountObserver>::get();
+}
+
 void USBMountObserver::Observe(NotificationType type,
                                const NotificationSource& source,
                                const NotificationDetails& details) {