Make content_browsertests support restarts across a test.

content/shell/shell_switches.cc

Index: content/shell/shell_switches.cc
===================================================================
--- content/shell/shell_switches.cc	(revision 152131)
+++ content/shell/shell_switches.cc	(working copy)
@@ -12,6 +12,9 @@
 // Tells Content Shell that it's running as a content_browsertest.
 const char kContentBrowserTest[] = "browser-test";
 
+// Makes Content Shell use the given path for its data directory.
+const char kContentShellDataPath[] = "data-path";
+
 // Request pages to be dumped as text once they finished loading.
 const char kDumpRenderTree[] = "dump-render-tree";