Bug 1770133 - part 2: Make IMEStateManager::sFocusedContent store i…

…t as `Element` r=m_kato

`nsFocusManager` defines that focused content is at least `dom::Element`.
So `IMEStateManager` can handle focused content with `dom::Element` too.

Additionally, this patch makes `IMEStateManager` methods take references instead
of pointers as far as possible if they just return error for `nullptr`.

Differential Revision: https://phabricator.services.mozilla.com/D147133

dom/base/nsFocusManager.cpp

@@ -5276,12 +5276,12 @@ void nsFocusManager::SetFocusedWindowInternal(nsPIDOMWindowOuter* aWindow,
   }
 }
 
-void nsFocusManager::NotifyOfReFocus(nsIContent& aContent) {
-  nsPIDOMWindowOuter* window = GetCurrentWindow(&aContent);
+void nsFocusManager::NotifyOfReFocus(Element& aElement) {
+  nsPIDOMWindowOuter* window = GetCurrentWindow(&aElement);
   if (!window || window != mFocusedWindow) {
     return;
   }
-  if (!aContent.IsInComposedDoc() || IsNonFocusableRoot(&aContent)) {
+  if (!aElement.IsInComposedDoc() || IsNonFocusableRoot(&aElement)) {
     return;
   }
   nsIDocShell* docShell = window->GetDocShell();
@@ -5296,7 +5296,7 @@ void nsFocusManager::NotifyOfReFocus(nsIContent& aContent) {
   if (!presContext) {
     return;
   }
-  IMEStateManager::OnReFocus(*presContext, aContent);
+  IMEStateManager::OnReFocus(*presContext, aElement);
 }
 
 void nsFocusManager::MarkUncollectableForCCGeneration(uint32_t aGeneration) {

dom/base/nsFocusManager.h

@@ -286,11 +286,11 @@ class nsFocusManager final : public nsIFocusManager,
   static InputContextAction::Cause GetFocusMoveActionCause(uint32_t aFlags);
 
   /**
-   * Notify of re-focus to same content.
+   * Notify of re-focus to same element.
    *
-   * aContent is focused content.
+   * aElement is focused element.
    */
-  MOZ_CAN_RUN_SCRIPT void NotifyOfReFocus(nsIContent& aContent);
+  MOZ_CAN_RUN_SCRIPT void NotifyOfReFocus(mozilla::dom::Element& aElement);
 
   static void MarkUncollectableForCCGeneration(uint32_t aGeneration);
 

dom/events/EventStateManager.cpp

@@ -5821,8 +5821,11 @@ void EventStateManager::ContentRemoved(Document* aDocument,
     element->LeaveLink(element->GetPresContext(Element::eForComposedDoc));
   }
 
-  if (RefPtr<nsPresContext> presContext = mPresContext) {
-    IMEStateManager::OnRemoveContent(*presContext, *aContent);
+  if (aContent->IsElement()) {
+    if (RefPtr<nsPresContext> presContext = mPresContext) {
+      IMEStateManager::OnRemoveContent(*presContext,
+                                       MOZ_KnownLive(*aContent->AsElement()));
+    }
   }
 
   // inform the focus manager that the content is being removed. If this