cros: Use runtime stylus detection for ash palette.

ash/common/system/chromeos/palette/palette_tray.h

Index: ash/common/system/chromeos/palette/palette_tray.h
diff --git a/ash/common/system/chromeos/palette/palette_tray.h b/ash/common/system/chromeos/palette/palette_tray.h
index 7dbc3c0baaf2f78480fba348673f456d0eae52c8..9633c35b729c6ad05b178ce0b9ad0437e777e633 100644
--- a/ash/common/system/chromeos/palette/palette_tray.h
+++ b/ash/common/system/chromeos/palette/palette_tray.h
@@ -16,6 +16,7 @@
 #include "ash/common/system/tray/tray_background_view.h"
 #include "base/macros.h"
 #include "base/memory/weak_ptr.h"
+#include "ui/events/devices/input_device_event_observer.h"
 
 namespace gfx {
 class Point;
@@ -38,6 +39,7 @@ class ASH_EXPORT PaletteTray : public TrayBackgroundView,
                                public SessionStateObserver,
                                public ShellObserver,
                                public PaletteToolManager::Delegate,
+                               public ui::InputDeviceEventObserver,
                                public views::TrayBubbleView::Delegate {
  public:
   explicit PaletteTray(WmShelf* wm_shelf);
@@ -78,6 +80,10 @@ class ASH_EXPORT PaletteTray : public TrayBackgroundView,
   bool ContainsPointInScreen(const gfx::Point& point);
 
  private:
+  // ui::InputDeviceObserver:
+  void OnTouchscreenDeviceConfigurationChanged() override;
+  void OnStylusStateChanged(ui::StylusState stylus_state) override;

[stevenjb, 2017/01/21 00:23:50]

It's a bit odd to have some overrides private and others public, but there seems
to already be precedent for that here. *shrug*. My preference would be to put
these with the public overrides, since the methods are effectively public.

[jdufault, 2017/01/25 00:53:15]

I think the rationale for making these private is that they are technically part
of the API, but not meant to be called directly and are an implementation
detail. Using that same line of thinking, most of the public overrides above
should actually be private as well.

wdyt?

[stevenjb, 2017/01/25 01:12:12]

Personally I prefer to keep public/private consistent with the parent class
declaration (i.e. generally public), since methods declared public in the parent
class are in fact public. Mostly we should be consistent.

+
   // views::TrayBubbleView::Delegate:
   void BubbleViewDestroyed() override;
   void OnMouseEnteredView() override;
@@ -103,9 +109,6 @@ class ASH_EXPORT PaletteTray : public TrayBackgroundView,
   // Sets the icon to visible if the palette can be used.
   void UpdateIconVisibility();
 
-  // Called when a stylus inserted or removed event is received.
-  void OnStylusStateChanged(ui::StylusState stylus_state);
-
   // Called when the palette enabled pref has changed.
   void OnPaletteEnabledPrefChanged(bool enabled);