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 5524ab5abc5a431015190ca70225784a8f8f852f..35069bb0f57b63ec9b010d072f7c1848346d308f 100644
--- a/ash/common/system/chromeos/palette/palette_tray.h
+++ b/ash/common/system/chromeos/palette/palette_tray.h
@@ -58,6 +58,10 @@ class ASH_EXPORT PaletteTray : public TrayBackgroundView,
   // Returns true if the shelf should not autohide.
   bool ShouldBlockShelfAutoHide() const;
 
+  // Opens up the palette if it is not already open. Returns true if the palette
+  // was opened.
+  bool ShowPalette();
+
  private:
   // views::TrayBubbleView::Delegate:
   void BubbleViewDestroyed() override;
@@ -93,7 +97,6 @@ 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_;