Implement issue 554 Add "ProcessDebuggerRequests" call to Debug Agent API

src/api.cc

Index: src/api.cc
diff --git a/src/api.cc b/src/api.cc
index ab5d0a5608e356ff79e2fdae76fe54234de042b2..25461019724892791a79ff493107e6c892306e7b 100644
--- a/src/api.cc
+++ b/src/api.cc
@@ -3744,6 +3744,11 @@ Local<Value> Debug::GetMirror(v8::Handle<v8::Value> obj) {
 bool Debug::EnableAgent(const char* name, int port, bool wait_for_connection) {
   return i::Debugger::StartAgent(name, port, wait_for_connection);
 }
+
+void Debug::ProcessDebugMessages() {
+  i::Execution::ProcessDebugMesssages(true);
+}
+
 #endif  // ENABLE_DEBUGGER_SUPPORT
 
 namespace internal {