Replace null ButtonListener*s with null Button::PressedCallbacks.

Bug: 772945
Change-Id: Ibeba130c3ad900eb279fd5b6e7e2ab0ba63f545b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2501061
Auto-Submit: Peter Kasting <pkasting@chromium.org>
Commit-Queue: James Cook <jamescook@chromium.org>
Reviewed-by: James Cook <jamescook@chromium.org>
Cr-Commit-Position: refs/heads/master@{#821295}

ash/hud_display/tab_strip.cc

@@ -79,7 +79,7 @@ END_METADATA
 HUDTabButton::HUDTabButton(Style style,
                            const DisplayMode display_mode,
                            const base::string16& text)
-    : views::LabelButton(nullptr, text),
+    : views::LabelButton(views::Button::PressedCallback(), text),
       style_(style),
       display_mode_(display_mode) {
   SetHorizontalAlignment(gfx::ALIGN_CENTER);

ash/shelf/shelf_button.cc

@@ -18,7 +18,7 @@ namespace ash {
 
 ShelfButton::ShelfButton(Shelf* shelf,
                          ShelfButtonDelegate* shelf_button_delegate)
-    : Button(nullptr),
+    : Button(Button::PressedCallback()),
       shelf_(shelf),
       shelf_button_delegate_(shelf_button_delegate) {
   DCHECK(shelf_button_delegate_);

ash/shelf/shelf_button_pressed_metric_tracker_unittest.cc

@@ -30,7 +30,7 @@ class DummyButton : public views::Button {
   DISALLOW_COPY_AND_ASSIGN(DummyButton);
 };
 
-DummyButton::DummyButton() : views::Button(nullptr) {}
+DummyButton::DummyButton() : views::Button(views::Button::PressedCallback()) {}
 
 // A simple light weight test double dummy for a ui::Event.
 class DummyEvent : public ui::Event {

ash/wm/overview/overview_session.cc

@@ -126,7 +126,7 @@ class AsyncWindowStateChangeObserver : public WindowStateObserver,
 // role button as the overview focus widget's contents.
 class OverviewFocusButton : public views::Button {
  public:
-  OverviewFocusButton() : views::Button(/*listener=*/nullptr) {
+  OverviewFocusButton() : views::Button(views::Button::PressedCallback()) {
     // Make this not focusable to avoid accessibility error since this view has
     // no accessible name.
     SetFocusBehavior(FocusBehavior::NEVER);