[Windows] Finish global and non-global media keys support on Windows.

chrome/browser/extensions/global_shortcut_listener_x11.cc

Index: chrome/browser/extensions/global_shortcut_listener_x11.cc
diff --git a/chrome/browser/extensions/global_shortcut_listener_x11.cc b/chrome/browser/extensions/global_shortcut_listener_x11.cc
index 0574c109841f41fd8dd987a1fc3d1670d99bd129..b0b73ccce57930fc47a34616e576bac94813e860 100644
--- a/chrome/browser/extensions/global_shortcut_listener_x11.cc
+++ b/chrome/browser/extensions/global_shortcut_listener_x11.cc
@@ -110,6 +110,13 @@ bool GlobalShortcutListenerX11::Dispatch(const base::NativeEvent& event) {
 void GlobalShortcutListenerX11::RegisterAccelerator(
     const ui::Accelerator& accelerator,
     GlobalShortcutListener::Observer* observer) {
+  if (registered_hot_keys_.find(accelerator) != registered_hot_keys_.end()) {
+    // The shortcut has already been registered. Some shortcuts, such as
+    // MediaKeys can have multiple targets, all keyed off of the same
+    // accelerator.
+    return;
+  }
+
   int modifiers = GetNativeModifiers(accelerator);
   KeyCode keycode = XKeysymToKeycode(x_display_, accelerator.key_code());
   base::X11ErrorTracker err_tracker;