Bug 1835353 - Make TextControlState notify IMEContentObserver of setting new value during no frame r=smaug

`IMEContentObserver` can observe the value changes only while the text control
has anonymous `<div>` element because it observers the DOM mutation.  The
anonymous `<div>` is alive (connected) only while the text control element
has a frame (recreated at each reframe).  Therefore, `IMEContentObserver`
cannot observe the value changed during reframing.

This patch makes `TextControlState` notify `IMEContentObserver` of setting
new value directly only when it does not have `mBoundFrame`.

Differential Revision: https://phabricator.services.mozilla.com/D179358

dom/html/TextControlState.cpp

@@ -6,6 +6,8 @@
 
 #include "TextControlState.h"
 #include "mozilla/Attributes.h"
+#include "mozilla/IMEContentObserver.h"
+#include "mozilla/IMEStateManager.h"
 #include "mozilla/TextInputListener.h"
 
 #include "nsCOMPtr.h"
@@ -2948,6 +2950,12 @@ bool TextControlState::SetValueWithoutTextEditor(
       if (mBoundFrame) {
         mBoundFrame->UpdateValueDisplay(true);
       }
+      // If the text control element has focus, IMEContentObserver is not
+      // observing the content changes due to no bound frame.  Therefore,
+      // we need to let IMEContentObserver know all values are being replaced.
+      else if (IMEContentObserver* observer = GetIMEContentObserver()) {
+        observer->OnTextControlValueChangedDuringNoFrame(mValue);
+      }
     }
 
     // If this is called as part of user input, we need to dispatch "input"
@@ -3040,4 +3048,12 @@ bool TextControlState::EditorHasComposition() {
   return mTextEditor && mTextEditor->IsIMEComposing();
 }
 
+IMEContentObserver* TextControlState::GetIMEContentObserver() const {
+  if (NS_WARN_IF(!mTextCtrlElement) ||
+      mTextCtrlElement != IMEStateManager::GetFocusedElement()) {
+    return nullptr;
+  }
+  return IMEStateManager::GetActiveContentObserver();
+}
+
 }  // namespace mozilla