ash/chromeos: Add shift-alt-p shortcut to open 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 5ef25fb55ffe2d48fb89850f6c1434f314584ca2..cbf1cc7217826e33cc267973e02af7e00e8fdf5a 100644
--- a/ash/common/system/chromeos/palette/palette_tray.h
+++ b/ash/common/system/chromeos/palette/palette_tray.h
@@ -59,6 +59,8 @@ class ASH_EXPORT PaletteTray : public TrayBackgroundView,
   // Returns true if the shelf should not autohide.
   bool ShouldBlockShelfAutoHide() const;
 
+  bool OpenBubble();
+
  private:
   // views::TrayBubbleView::Delegate:
   void BubbleViewDestroyed() override;
@@ -94,7 +96,6 @@ class ASH_EXPORT PaletteTray : public TrayBackgroundView,
   // Called when the palette enabled pref has changed.
   void OnPaletteEnabledPrefChanged(bool enabled);
 
-  bool OpenBubble();
   void AddToolsToView(views::View* host);
 
   std::unique_ptr<PaletteToolManager> palette_tool_manager_;