Adds the concept of a 'safe mode' hotkey start

chrome/installer/util/browser_distribution.h

Index: chrome/installer/util/browser_distribution.h
===================================================================
--- chrome/installer/util/browser_distribution.h	(revision 232633)
+++ chrome/installer/util/browser_distribution.h	(working copy)
@@ -161,6 +161,9 @@
 
   virtual bool HasUserExperiments();
 
+  // Returning zero means that there is no hotkey.
+  virtual int GetSafeModeHotkey();

[robertshield, 2013/11/04 02:19:55]

should this return a uint32 instead?

[grt (UTC plus 2), 2013/11/04 15:25:14]

what about uint16 (IShellLink::SetHotkey takes a WORD)?

[cpu_(ooo_6.6-7.5), 2013/11/04 19:10:57]

Done.

Since I am not ifdefing for windows I rather keep it dword size, also seems that
RegisterHotkey (if we were to ever use it) is hard to pack in 16 bits (although
technically doable).

Going with Robert's uint32. 

+
  protected:
   explicit BrowserDistribution(Type type);