Refactor shutdown code to allow win/linux to run after last browser closes.

chrome/common/chrome_switches.cc

Index: chrome/common/chrome_switches.cc
diff --git a/chrome/common/chrome_switches.cc b/chrome/common/chrome_switches.cc
index ccef4750a03212805988877da0ded3ea04e18acc..3c4255a3216791c97a87e0fbde09b760f3ed3d77 100644
--- a/chrome/common/chrome_switches.cc
+++ b/chrome/common/chrome_switches.cc
@@ -564,6 +564,9 @@ const char kIssue35198Permission[]          = "issue35198-permission";
 // Specifies the flags passed to JS engine
 const char kJavaScriptFlags[]               = "js-flags";
 
+// Used for testing - keeps browser alive after last browser window closes.
+const char kKeepAliveForTest[]              = "keep-alive-for-test";
+
 // Load an extension from the specified directory.
 const char kLoadExtension[]                 = "load-extension";