dark_mode: Collapse button can be always enabled.

The chromevox navigation of collapse button has been improved at
crrev.com/c/2032508. The collapse button is actually always enabled now.
Remove the useless logic of it.

Bug: 1131543
Change-Id: I3cb398ec7aed15f9eebcb53c567540b7ee3ac586
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2488385
Commit-Queue: Min Chen <minch@chromium.org>
Reviewed-by: Ahmed Fakhry <afakhry@chromium.org>
Cr-Commit-Position: refs/heads/master@{#819943}

ash/system/unified/collapse_button.cc

@@ -16,7 +16,11 @@ namespace ash {
 
 CollapseButton::CollapseButton(views::ButtonListener* listener)
     : CustomShapeButton(listener) {
-  UpdateVectorIcon();
+  SetImage(views::Button::STATE_NORMAL,
+           gfx::CreateVectorIcon(
+               kUnifiedMenuExpandIcon,
+               AshColorProvider::Get()->GetContentLayerColor(
+                   AshColorProvider::ContentLayerType::kIconColorPrimary)));
 }
 
 CollapseButton::~CollapseButton() = default;
@@ -58,14 +62,4 @@ const char* CollapseButton::GetClassName() const {
   return "CollapseButton";
 }
 
-void CollapseButton::UpdateVectorIcon() {
-  const SkColor icon_color = AshColorProvider::Get()->GetContentLayerColor(
-      AshColorProvider::ContentLayerType::kIconColorPrimary);
-  SetImage(views::Button::STATE_NORMAL,
-           gfx::CreateVectorIcon(
-               kUnifiedMenuExpandIcon,
-               GetEnabled() ? icon_color
-                            : AshColorProvider::GetDisabledColor(icon_color)));
-}
-
 }  // namespace ash

ash/system/unified/collapse_button.h

@@ -6,7 +6,6 @@
 #define ASH_SYSTEM_UNIFIED_COLLAPSE_BUTTON_H_
 
 #include "ash/system/unified/custom_shape_button.h"
-#include "base/bind.h"
 
 namespace ash {
 
@@ -29,16 +28,7 @@ class CollapseButton : public CustomShapeButton {
   const char* GetClassName() const override;
 
  private:
-  // Update the vector icon on initializing CollapseButton or when the |Enabled|
-  // property of CollapseButton changes. The vector icon will have different
-  // colors on the |Enabled| property.
-  void UpdateVectorIcon();
-
   double expanded_amount_ = 1.0;
-  views::PropertyChangedSubscription enabled_changed_subscription_ =
-      AddEnabledChangedCallback(
-          base::BindRepeating(&CollapseButton::UpdateVectorIcon,
-                              base::Unretained(this)));
 
   DISALLOW_COPY_AND_ASSIGN(CollapseButton);
 };