Introduce ThreadedInputConnection behind a switch

content/renderer/input/render_widget_input_handler.cc

Index: content/renderer/input/render_widget_input_handler.cc
diff --git a/content/renderer/input/render_widget_input_handler.cc b/content/renderer/input/render_widget_input_handler.cc
index d5d5255c02f9c864a383a94ca1745f640d47461b..13443c75bf400afa9e16d2e084d8eefdf5200fe7 100644
--- a/content/renderer/input/render_widget_input_handler.cc
+++ b/content/renderer/input/render_widget_input_handler.cc
@@ -9,6 +9,7 @@
 #include <utility>
 
 #include "base/auto_reset.h"
+#include "base/command_line.h"
 #include "base/metrics/histogram_macros.h"
 #include "base/trace_event/trace_event_synthetic_delay.h"
 #include "build/build_config.h"
@@ -17,6 +18,7 @@
 #include "content/common/input/input_event_ack.h"
 #include "content/common/input/input_event_ack_state.h"
 #include "content/common/input/web_input_event_traits.h"
+#include "content/public/common/content_switches.h"
 #include "content/renderer/gpu/render_widget_compositor.h"
 #include "content/renderer/ime_event_guard.h"
 #include "content/renderer/input/render_widget_input_handler_delegate.h"
@@ -208,10 +210,12 @@ void RenderWidgetInputHandler::HandleInputEvent(
 
 #if defined(OS_ANDROID)
   bool from_ime = false;
+  bool use_ime_thread = base::CommandLine::ForCurrentProcess()->HasSwitch(
+      switches::kUseImeThread);
 
   // For most keyboard events, we want the change source to be FROM_IME because
   // we don't need to update IME states in AdapterInputConnection.
-  if (WebInputEvent::isKeyboardEventType(input_event.type)) {
+  if (!use_ime_thread && WebInputEvent::isKeyboardEventType(input_event.type)) {
     const WebKeyboardEvent& key_event =
         *static_cast<const WebKeyboardEvent*>(&input_event);
     // TODO(changwan): this if-condition is a stop-gap solution to update IME
@@ -226,11 +230,13 @@ void RenderWidgetInputHandler::HandleInputEvent(
         key_event.nativeKeyCode != AKEYCODE_DPAD_LEFT &&
         key_event.nativeKeyCode != AKEYCODE_DPAD_RIGHT &&
         key_event.nativeKeyCode != AKEYCODE_DPAD_UP &&
-        key_event.nativeKeyCode != AKEYCODE_DPAD_DOWN)
+        key_event.nativeKeyCode != AKEYCODE_DPAD_DOWN) {
       from_ime = true;
+    }
   }
 
-  ImeEventGuard guard(widget_, false, from_ime);
+  ImeEventGuard guard(widget_);
+  guard.set_from_ime(from_ime);
 #endif
 
   base::TimeTicks start_time;