Adding metadata to AssistantButton

This is part of the "Views Posse" effort. See this document:
https://docs.google.com/document/d/1Rst3792TjXtVA8k8GXaPD8MnuB1JAneSOpIILdA4268/edit?usp=sharing

Bug: 1159562
Test: build
Change-Id: Id54167a8b23b0e2cf0046de263510c7e3526f470
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2596711Reviewed-by: Allen Bauer <kylixrd@chromium.org>
Reviewed-by: Mitsuru Oshima <oshima@chromium.org>
Commit-Queue: Shengsong Tan <sstan@google.com>
Cr-Commit-Position: refs/heads/master@{#840892}

ash/assistant/ui/base/assistant_button.cc

@@ -14,6 +14,7 @@
 #include "ui/views/animation/flood_fill_ink_drop_ripple.h"
 #include "ui/views/animation/ink_drop_impl.h"
 #include "ui/views/controls/highlight_path_generator.h"
+#include "ui/views/metadata/metadata_impl_macros.h"
 
 namespace ash {
 
@@ -87,10 +88,6 @@ std::unique_ptr<AssistantButton> AssistantButton::Create(
   return button;
 }
 
-const char* AssistantButton::GetClassName() const {
-  return "AssistantButton";
-}
-
 void AssistantButton::OnBoundsChanged(const gfx::Rect& previous_bounds) {
   // Note that the current assumption is that button bounds are square.
   DCHECK_EQ(width(), height());
@@ -127,4 +124,7 @@ void AssistantButton::OnButtonPressed() {
   listener_->OnButtonPressed(id_);
 }
 
+BEGIN_METADATA(AssistantButton, views::ImageButton)
+END_METADATA
+
 }  // namespace ash

ash/assistant/ui/base/assistant_button.h

@@ -13,6 +13,7 @@
 #include "third_party/skia/include/core/SkColor.h"
 #include "ui/gfx/color_palette.h"
 #include "ui/views/controls/button/image_button.h"
+#include "ui/views/metadata/metadata_header_macros.h"
 
 namespace gfx {
 struct VectorIcon;
@@ -30,6 +31,8 @@ enum class AssistantButtonId;
 class COMPONENT_EXPORT(ASSISTANT_UI) AssistantButton
     : public views::ImageButton {
  public:
+  METADATA_HEADER(AssistantButton);
+
   // Initialization parameters for customizing the Assistant button.
   struct InitParams {
     InitParams();
@@ -68,8 +71,6 @@ class COMPONENT_EXPORT(ASSISTANT_UI) AssistantButton
 
   AssistantButtonId GetAssistantButtonId() const { return id_; }
 
-  // views::Button:
-  const char* GetClassName() const override;
   void OnBoundsChanged(const gfx::Rect& previous_bounds) override;
   std::unique_ptr<views::InkDrop> CreateInkDrop() override;
   std::unique_ptr<views::InkDropHighlight> CreateInkDropHighlight()