Add simple cache backend experiment hidden behind a flag.

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 a4e91b3564101fd066c12f12cab4141f957e922d..cd522cffb9efb6d452e4a585d8019c10c0aaa3d6 100644
--- a/chrome/common/chrome_switches.cc
+++ b/chrome/common/chrome_switches.cc
@@ -1374,6 +1374,9 @@ const char kUserDataDir[]                   = "user-data-dir";
 // Uses the ClientLogin signin flow instead of the web-based signin flow.
 const char kUseClientLoginSigninFlow[]      = "use-client-login-signin-flow";
 
+// Uses experimental simple cache backend if possible.
+const char kUseSimpleCacheBackend[]         = "use-simple-cache-backend";
+
 // Specifies a custom URL for the server which reports variation data to the
 // client. Specifying this switch enables the Variations service on
 // unofficial builds. See variations_service.cc.