Introduce ThreadedInputConnection behind a switch

content/renderer/render_widget.h

Index: content/renderer/render_widget.h
diff --git a/content/renderer/render_widget.h b/content/renderer/render_widget.h
index a7bf289d27d17651a50b790bc45ba742111eab0d..d86e131628187fc42de3a6d741ee1f848c460d18 100644
--- a/content/renderer/render_widget.h
+++ b/content/renderer/render_widget.h
@@ -319,6 +319,9 @@ class CONTENT_EXPORT RenderWidget
   // |policy| see the comment on MessageDeliveryPolicy.
   void QueueMessage(IPC::Message* msg, MessageDeliveryPolicy policy);
 
+  // Check whether IME thread is being used or not.
+  bool IsUsingImeThread();
+
   // Handle start and finish of IME event guard.
   void OnImeEventGuardStart(ImeEventGuard* guard);
   void OnImeEventGuardFinish(ImeEventGuard* guard);
@@ -461,6 +464,12 @@ class CONTENT_EXPORT RenderWidget
 
   // Called by the browser process for every required IME acknowledgement.
   void OnImeEventAck();
+
+  // Called by the browser process to update text input state.
+  void OnRequestTextInputStateUpdate();
+
+  // Called by the browser process to disable IME thread.
+  void OnDisableImeThread();
 #endif
 
   // Notify the compositor about a change in viewport size. This should be
@@ -722,6 +731,9 @@ class CONTENT_EXPORT RenderWidget
   // by script etc., not by user input.
   bool text_field_is_dirty_;
 
+  // True if we disabled IME thread due to an error.
+  bool ime_thread_disabled_due_to_error_;
+
   // Stores the history of text input infos from the last ACK'ed one from the
   // current one. The size is the number of pending ACKs plus one, since we
   // intentionally keep the last ack'd value to know what the browser is