Track when profiles are last used.

chrome/browser/profiles/profile_info_interface.h

Index: chrome/browser/profiles/profile_info_interface.h
diff --git a/chrome/browser/profiles/profile_info_interface.h b/chrome/browser/profiles/profile_info_interface.h
index 6114712d2c02473c06dad44692be2a01ac9aab0e..3cec13ab931ab06b082827d51a284af30e96ab0c 100644
--- a/chrome/browser/profiles/profile_info_interface.h
+++ b/chrome/browser/profiles/profile_info_interface.h
@@ -8,6 +8,10 @@
 #include "base/files/file_path.h"
 #include "base/strings/string16.h"
 
+namespace base {
+class Time;
+}
+
 namespace gfx {
 class Image;
 }
@@ -22,6 +26,8 @@ class ProfileInfoInterface {
   virtual size_t GetIndexOfProfileWithPath(
       const base::FilePath& profile_path) const = 0;
 
+  virtual base::Time GetProfileActiveTimeAtIndex(size_t index) const = 0;
+
   virtual base::string16 GetNameOfProfileAtIndex(size_t index) const = 0;
 
   virtual base::string16 GetShortcutNameOfProfileAtIndex(