Flush UI message loop before quitting

Cookies were not flushed on application exit because objects deleted
lazy on the UI-thread never had their destructors called because we
did not flush the queue on exit.

Change-Id: If53cdb5547e15a9f39de8b99b1da313e307b1c90
Reviewed-by: Jocelyn Turcotte <jocelyn.turcotte@digia.com>

src/core/web_engine_context.cpp

@@ -41,6 +41,7 @@
 #include "base/base_switches.h"
 #include "base/command_line.h"
 #include "base/files/file_path.h"
+#include "base/message_loop/message_loop.h"
 #include "base/run_loop.h"
 #include "base/threading/thread_restrictions.h"
 #include "cc/base/switches.h"
@@ -93,6 +94,9 @@ void destroyContext()
 
 WebEngineContext::~WebEngineContext()
 {
+    base::MessagePump::Delegate *delegate = m_runLoop->loop_;
+    // Flush the UI message loop before quitting.
+    while (delegate->DoWork()) { }
     GLContextHelper::destroy();
     m_runLoop->AfterRun();
 }