Only block internal touchpad and allow external mice to continue working in maximize mode.

ash/wm/maximize_mode/maximize_mode_event_blocker.h

Index: ash/wm/maximize_mode/maximize_mode_event_blocker.h
diff --git a/ash/wm/maximize_mode/maximize_mode_event_blocker.h b/ash/wm/maximize_mode/maximize_mode_event_blocker.h
index 9e4a1a0bfa043fadc7e26af67621c719a8c173f6..e487f776bf2d76eafb043581163b2102d9b40e90 100644
--- a/ash/wm/maximize_mode/maximize_mode_event_blocker.h
+++ b/ash/wm/maximize_mode/maximize_mode_event_blocker.h
@@ -5,6 +5,8 @@
 #ifndef ASH_WM_MAXIMIZE_MODE_MAXIMIZE_MODE_EVENT_BLOCKER_H_
 #define ASH_WM_MAXIMIZE_MODE_MAXIMIZE_MODE_EVENT_BLOCKER_H_
 
+#include <set>
+
 #include "ash/shell_observer.h"
 #include "base/macros.h"
 #include "base/memory/scoped_vector.h"
@@ -32,6 +34,10 @@ class MaximizeModeEventBlocker : public ShellObserver {
 
   ScopedVector<aura::ScopedWindowTargeter> targeters_;
 
+  // Tracks the device ids of internal input devices. Events from these are
+  // blocked while this object is instantiated.
+  std::set<int> internal_device_ids_;
+
   DISALLOW_COPY_AND_ASSIGN(MaximizeModeEventBlocker);
 };