linux: Fixes a racy crash by key input at termination.

It seems that it's possible that GDK events happen while we're going
to unregister the GDK event handler, and the code must be thread-safe.
(A gpointer |data| in the old code seems pointing to the deleted object.)

This CL removes use of |data| pointer and makes the code thread-safe
without adding any mutex.

BUG=417210

Review URL: https://codereview.chromium.org/610523002

Cr-Commit-Position: refs/heads/master@{#297112}

chrome/browser/ui/libgtk2ui/gtk2_event_loop.cc

@@ -20,7 +20,7 @@ Gtk2EventLoop* Gtk2EventLoop::GetInstance() {
 }
 
 Gtk2EventLoop::Gtk2EventLoop() {
-  gdk_event_handler_set(GdkEventTrampoline, this, NULL);
+  gdk_event_handler_set(DispatchGdkEvent, NULL, NULL);
 }
 
 Gtk2EventLoop::~Gtk2EventLoop() {
@@ -29,12 +29,7 @@ Gtk2EventLoop::~Gtk2EventLoop() {
 }
 
 // static
-void Gtk2EventLoop::GdkEventTrampoline(GdkEvent* event, gpointer data) {
-  Gtk2EventLoop* loop = reinterpret_cast<Gtk2EventLoop*>(data);
-  loop->DispatchGdkEvent(event);
-}
-
-void Gtk2EventLoop::DispatchGdkEvent(GdkEvent* gdk_event) {
+void Gtk2EventLoop::DispatchGdkEvent(GdkEvent* gdk_event, gpointer) {
   switch (gdk_event->type) {
     case GDK_KEY_PRESS:
     case GDK_KEY_RELEASE:
@@ -47,6 +42,7 @@ void Gtk2EventLoop::DispatchGdkEvent(GdkEvent* gdk_event) {
   gtk_main_do_event(gdk_event);
 }
 
+// static
 void Gtk2EventLoop::ProcessGdkEventKey(const GdkEventKey& gdk_event_key) {
   // This function translates GdkEventKeys into XKeyEvents and puts them to
   // the X event queue.

chrome/browser/ui/libgtk2ui/gtk2_event_loop.h

@@ -25,10 +25,8 @@ class Gtk2EventLoop {
   Gtk2EventLoop();
   ~Gtk2EventLoop();
 
-  static void GdkEventTrampoline(GdkEvent* event, gpointer data);
-
-  void DispatchGdkEvent(GdkEvent* gdk_event);
-  void ProcessGdkEventKey(const GdkEventKey& gdk_event_key);
+  static void DispatchGdkEvent(GdkEvent* gdk_event, gpointer);
+  static void ProcessGdkEventKey(const GdkEventKey& gdk_event_key);
 
   DISALLOW_COPY_AND_ASSIGN(Gtk2EventLoop);
 };