Bug 1765109 - Make TextEventDispatcher::MaybeQueryWritingModeAtSelection not try to query selection if it's unavailable r=m_kato

We resolve editing commands on Linux and macOS to respect the system settings
of every key press when an `eKeyPress` event is sent to a remote process, and
it requires `WritingMode` at selection for arrow key handling for example.
Therefore, the parent process try to get the information.

However, in the case, the query succeeds only when IME has focus since
`ContentCacheInParent` does not have any data when IME does not have focus.
Therefore, `TextEventDispatcher::MaybeQueryWritingModeAtSelection` should
check the IME state before dispatching `eQuerySelectedText` event to avoid
the warnings and unnecessary runtime cost.

Differential Revision: https://phabricator.services.mozilla.com/D143901

widget/TextEventDispatcher.cpp

@@ -240,6 +240,16 @@ Maybe<WritingMode> TextEventDispatcher::MaybeQueryWritingModeAtSelection()
     return Nothing();
   }
 
+  // If a remote content has focus and IME does not have focus, it's going to
+  // fail eQuerySelectedText in ContentCacheParent.  For avoiding to waste
+  // unnecessary runtime cost and to prevent unnecessary warnings, we should
+  // not dispatch the event in the case.
+  const InputContext inputContext = mWidget->GetInputContext();
+  if (XRE_IsE10sParentProcess() && inputContext.IsOriginContentProcess() &&
+      !inputContext.mIMEState.IsEditable()) {
+    return Nothing();
+  }
+
   WidgetQueryContentEvent querySelectedTextEvent(true, eQuerySelectedText,
                                                  mWidget);
   nsEventStatus status = nsEventStatus_eIgnore;