part 4 of the arrow button implementation

This CL is the forth part of code to implement the arrow button in
the overflow bubble view.
See more details from the below doc link:
https://docs.google.com/document/d/1dO4H_4T6ttWFc75nCNi2Uh18k-3_M8-eOHcfMTcNwd0/edit?usp=sharing

Bug: 918024
Change-Id: I2ee940845c61a52e1250487c8dce1e942759adb9
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1703268
Commit-Queue: Andrew Xu <andrewxu@chromium.org>
Reviewed-by: Mitsuru Oshima (Slow - traveling) <oshima@chromium.org>
Cr-Commit-Position: refs/heads/master@{#683031}

ash/shelf/overflow_bubble_view.h

@@ -23,7 +23,7 @@ class ASH_EXPORT OverflowBubbleView : public ShelfBubble,
   enum LayoutStrategy {
     // The arrow buttons are not shown. It means that there is enough space to
     // accommodate all of shelf icons.
-    NOT_SHOW_ARROW_BUTTON,
+    NOT_SHOW_ARROW_BUTTONS,
 
     // Only the left arrow button is shown.
     SHOW_LEFT_ARROW_BUTTON,
@@ -52,6 +52,9 @@ class ASH_EXPORT OverflowBubbleView : public ShelfBubble,
   int ScrollByXOffset(float x_offset, bool animating);
   int ScrollByYOffset(float y_offset, bool animating);
 
+  int GetFirstVisibleIndexForTest() const;
+  int GetLastVisibleIndexForTest() const;
+
   // views::BubbleDialogDelegateView:
   gfx::Rect GetBubbleBounds() override;
   bool CanActivate() const override;
@@ -74,6 +77,8 @@ class ASH_EXPORT OverflowBubbleView : public ShelfBubble,
   // Minimum margin around the bubble so that it doesn't hug the screen edges.
   static constexpr int kMinimumMargin = 8;
 
+  static constexpr int kFadingZone = 16;
+
  private:
   friend class OverflowBubbleViewTestAPI;
 

ash/test/ash_test_base.cc

@@ -509,12 +509,12 @@ void AshTestBase::SwapPrimaryDisplay() {
       display_manager()->GetSecondaryDisplay().id());
 }
 
-display::Display AshTestBase::GetPrimaryDisplay() {
+display::Display AshTestBase::GetPrimaryDisplay() const {
   return display::Screen::GetScreen()->GetDisplayNearestWindow(
       Shell::GetPrimaryRootWindow());
 }
 
-display::Display AshTestBase::GetSecondaryDisplay() {
+display::Display AshTestBase::GetSecondaryDisplay() const {
   return ash_test_helper_.GetSecondaryDisplay();
 }
 

ash/test/ash_test_base.h

@@ -258,8 +258,8 @@ class AshTestBase : public testing::Test {
   // Swap the primary display with the secondary.
   void SwapPrimaryDisplay();
 
-  display::Display GetPrimaryDisplay();
-  display::Display GetSecondaryDisplay();
+  display::Display GetPrimaryDisplay() const;
+  display::Display GetSecondaryDisplay() const;
 
  private:
   void CreateWindowTreeIfNecessary();

ash/test/ash_test_helper.cc

@@ -299,7 +299,7 @@ aura::Window* AshTestHelper::CurrentContext() {
   return root_window;
 }
 
-display::Display AshTestHelper::GetSecondaryDisplay() {
+display::Display AshTestHelper::GetSecondaryDisplay() const {
   return Shell::Get()->display_manager()->GetSecondaryDisplay();
 }
 

ash/test/ash_test_helper.h

@@ -105,7 +105,7 @@ class AshTestHelper {
     return test_views_delegate_.get();
   }
 
-  display::Display GetSecondaryDisplay();
+  display::Display GetSecondaryDisplay() const;
 
   TestSessionControllerClient* test_session_controller_client() {
     return session_controller_client_.get();