Made MessagePump a non-thread safe class.

base/message_loop/message_pump_mac.mm

Index: base/message_loop/message_pump_mac.mm
diff --git a/base/message_loop/message_pump_mac.mm b/base/message_loop/message_pump_mac.mm
index f46d7a8d836b2892cc3e041a2ff96969e81a341f..f885fbf5f6bbb9d53fc1d24363c0f427699ace6c 100644
--- a/base/message_loop/message_pump_mac.mm
+++ b/base/message_loop/message_pump_mac.mm
@@ -616,6 +616,9 @@ void MessagePumpNSApplication::Quit() {
 MessagePumpCrApplication::MessagePumpCrApplication() {
 }
 
+MessagePumpCrApplication::~MessagePumpCrApplication() {
+}
+
 // Prevents an autorelease pool from being created if the app is in the midst of
 // handling a UI event because various parts of AppKit depend on objects that
 // are created while handling a UI event to be autoreleased in the event loop.