Adding the Copresence RpcHandler and HttpPost helper.

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 1e958f744fbe56154301abc1140ddf84f9bbdc4d..d1bc353209aa67f72b32f419f2d380ee5f981af9 100644
--- a/chrome/common/chrome_switches.cc
+++ b/chrome/common/chrome_switches.cc
@@ -778,10 +778,12 @@ const char kKioskMode[]                     = "kiosk";
 // See http://crbug.com/31395.
 const char kKioskModePrinting[]             = "kiosk-printing";
 
-// Use this server address ledger.
+// Address for the ledger (Copresence) server.
+// Ledger is deprecated; use the chrome.copresence API instead.
 const char kLedgerServer[]                  = "ledger-server";
 
-// Use this tracing token for ledger.
+// Tracing token for calls to the ledger (Copresence) server.
+// Ledger is deprecated; use the chrome.copresence API instead.
 const char kLedgerTracingToken[]            = "ledger-tracing-token";
 
 // Causes Chrome to attempt to get metadata from the webstore for the