Bug 1234120 part.1 IMEHandler should request all notifications which are requested by either IMMHander or TSFTextStore when IMM is available in TSF mode r=m_kato

widget/IMEData.h

@@ -71,6 +71,11 @@ struct nsIMEUpdatePreference final
   {
   }
 
+  nsIMEUpdatePreference operator|(const nsIMEUpdatePreference& aOther) const
+  {
+    return nsIMEUpdatePreference(aOther.mWantUpdates | mWantUpdates);
+  }
+
   void DontNotifyChangesCausedByComposition()
   {
     mWantUpdates &= ~DEFAULT_CONDITIONS_OF_NOTIFYING_CHANGES;

widget/windows/WinIMEHandler.cpp

@@ -334,7 +334,16 @@ IMEHandler::GetUpdatePreference()
 
 #ifdef NS_ENABLE_TSF
   if (IsTSFAvailable()) {
-    return TSFTextStore::GetIMEUpdatePreference();
+    if (!sIsIMMEnabled) {
+      return TSFTextStore::GetIMEUpdatePreference();
+    }
+    // Even if TSF is available, the active IME may be an IMM-IME.
+    // Unfortunately, changing the result of GetUpdatePreference() while an
+    // editor has focus isn't supported by IMEContentObserver nor
+    // ContentCacheInParent.  Therefore, we need to request whole notifications
+    // which are necessary either IMMHandler or TSFTextStore.
+    return IMMHandler::GetIMEUpdatePreference() |
+             TSFTextStore::GetIMEUpdatePreference();
   }
 #endif //NS_ENABLE_TSF