Fix appearance of disabled VectorIconButtons.

Ironically, removing OnEnabledChanged() fixes this bug. Not calling
through to the parent class's implementation was problematic, but it
turns out that handling changes to the enable state isn't necessary
anyway since that's done with the state parameter of
ImageButton::SetImage().

BUG=645353

Review-Url: https://codereview.chromium.org/2340503002
Cr-Commit-Position: refs/heads/master@{#418431}

ui/views/controls/button/vector_icon_button.cc

@@ -46,10 +46,6 @@ void VectorIconButton::SetIcon(gfx::VectorIconId id) {
   }
 }
 
-void VectorIconButton::OnEnabledChanged() {
-  OnThemeChanged();
-}
-
 void VectorIconButton::OnThemeChanged() {
   SkColor icon_color =
       color_utils::DeriveDefaultIconColor(delegate_->GetVectorIconBaseColor());

ui/views/controls/button/vector_icon_button.h

@@ -28,7 +28,6 @@ class VIEWS_EXPORT VectorIconButton : public views::ImageButton {
   void SetIcon(gfx::VectorIconId id);
 
   // views::ImageButton:
-  void OnEnabledChanged() override;
   void OnThemeChanged() override;
   void OnNativeThemeChanged(const ui::NativeTheme* theme) override;