Add a new GetInstance() method for singleton classes used in chrome/browser files.

chrome/browser/browser_main_gtk.cc

Index: chrome/browser/browser_main_gtk.cc
diff --git a/chrome/browser/browser_main_gtk.cc b/chrome/browser/browser_main_gtk.cc
index 924bffd2b6684ac9d395b24740bfa9e9c8315885..ec73aafd72f235b5169d560452ce11a0db39687f 100644
--- a/chrome/browser/browser_main_gtk.cc
+++ b/chrome/browser/browser_main_gtk.cc
@@ -86,9 +86,9 @@ void BrowserMainPartsGtk::SetupSandbox() {
     sandbox_cmd = sandbox_binary;
 
   // Tickle the sandbox host and zygote host so they fork now.
-  RenderSandboxHostLinux* shost = Singleton<RenderSandboxHostLinux>::get();
+  RenderSandboxHostLinux* shost = RenderSandboxHostLinux::GetInstance();
   shost->Init(sandbox_cmd);
-  ZygoteHost* zhost = Singleton<ZygoteHost>::get();
+  ZygoteHost* zhost = ZygoteHost::GetInstance();
   zhost->Init(sandbox_cmd);
 }