Make blink::PopupOpeningObserver a GarbageCollectedMixin

All of PopupOpeningObserver implementors are on GC heap, and having
raw pointers to them is dangerous.

This CL is a preparation to make blink::FileInputType a
PopupOpeningObserver.

Bug: 637639
Change-Id: Iee014462716cc3c3de91ddf365ab8644e2de5f2e
Reviewed-on: https://chromium-review.googlesource.com/1113084
Commit-Queue: Kent Tamura <tkent@chromium.org>
Reviewed-by: Keishi Hattori <keishi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#569983}

third_party/blink/renderer/core/html/forms/spin_button_element.h

@@ -36,6 +36,8 @@ namespace blink {
 
 class CORE_EXPORT SpinButtonElement final : public HTMLDivElement,
                                             public PopupOpeningObserver {
+  USING_GARBAGE_COLLECTED_MIXIN(SpinButtonElement);
+
  public:
   enum UpDownState {
     kIndeterminate,  // Hovered, but the event is not handled.

third_party/blink/renderer/core/page/chrome_client_impl.cc

@@ -159,6 +159,11 @@ ChromeClientImpl* ChromeClientImpl::Create(WebViewImpl* web_view) {
   return new ChromeClientImpl(web_view);
 }
 
+void ChromeClientImpl::Trace(Visitor* visitor) {
+  visitor->Trace(popup_opening_observers_);
+  ChromeClient::Trace(visitor);
+}
+
 WebViewImpl* ChromeClientImpl::GetWebView() const {
   return web_view_;
 }
@@ -1097,8 +1102,9 @@ void ChromeClientImpl::UnregisterPopupOpeningObserver(
 }
 
 void ChromeClientImpl::NotifyPopupOpeningObservers() const {
-  const Vector<PopupOpeningObserver*> observers(popup_opening_observers_);
-  for (auto* const observer : observers)
+  const HeapVector<Member<PopupOpeningObserver>> observers(
+      popup_opening_observers_);
+  for (const auto& observer : observers)
     observer->WillOpenPopup();
 }
 

third_party/blink/renderer/core/page/chrome_client_impl.h

@@ -52,6 +52,7 @@ class CORE_EXPORT ChromeClientImpl final : public ChromeClient {
  public:
   static ChromeClientImpl* Create(WebViewImpl*);
   ~ChromeClientImpl() override;
+  void Trace(Visitor* visitor) override;
 
   WebViewImpl* GetWebView() const override;
 
@@ -243,7 +244,7 @@ class CORE_EXPORT ChromeClientImpl final : public ChromeClient {
   WebAutofillClient* AutofillClientFromFrame(LocalFrame*);
 
   WebViewImpl* web_view_;  // Weak pointer.
-  Vector<PopupOpeningObserver*> popup_opening_observers_;
+  HeapVector<Member<PopupOpeningObserver>> popup_opening_observers_;
   Cursor last_set_mouse_cursor_for_testing_;
   bool cursor_overridden_;
   bool did_request_non_empty_tool_tip_;

third_party/blink/renderer/core/page/popup_opening_observer.h

@@ -27,10 +27,11 @@
 #define THIRD_PARTY_BLINK_RENDERER_CORE_PAGE_POPUP_OPENING_OBSERVER_H_
 
 #include "third_party/blink/renderer/core/core_export.h"
+#include "third_party/blink/renderer/platform/heap/handle.h"
 
 namespace blink {
 
-class CORE_EXPORT PopupOpeningObserver {
+class CORE_EXPORT PopupOpeningObserver : public GarbageCollectedMixin {
  public:
   virtual void WillOpenPopup() = 0;