Makes delay commitText/setComposition can deal with empty text/composition.

chrome/browser/ui/input_method/input_method_engine.cc

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "chrome/browser/ui/input_method/input_method_engine.h"
 
 #include "chrome/browser/ui/browser_finder.h"
 #include "chrome/browser/ui/browser_window.h"
 #include "chrome/browser/ui/tabs/tab_strip_model.h"
 #include "chrome/common/url_constants.h"
@@ skipping 128 matching lines @@
   // Use a black thin underline by default.
   if (composition_.underlines.empty()) {
     composition_.underlines.push_back(
         ui::CompositionUnderline(0, composition_.text.length(), SK_ColorBLACK,
                                  false /* thick */, SK_ColorTRANSPARENT));
   }
 
   ui::IMEInputContextHandlerInterface* input_context =
       ui::IMEBridge::Get()->GetInputContextHandler();
   // If the IME extension is handling key event, hold the composition text
-  // until the key event is handled.
-  if (input_context && !handling_key_event_) {
+  // until the key event is handled. However, if trying to clear the
+  // composition, do UpdateCompositionText at once.
+  if ((input_context && !handling_key_event_) || composition_.text.empty()) {
     input_context->UpdateCompositionText(composition_, cursor_pos, is_visible);

[Azure Wei, 2016/11/23 07:53:42]

In UpdateCompositionText(), we would send a faked key event:
https://cs.chromium.org/chromium/src/ui/base/ime/input_method_base.cc?q=Updat...
Not sure if this is a safe when handing key event.

[Shu Chen, 2016/11/24 02:57:57]

Done.

     composition_.Clear();
   }
 }
 
 void InputMethodEngine::CommitTextToInputContext(int context_id,
                                                  const std::string& text) {
   // Append the text to the buffer, as it allows committing text multiple times
   // when processing a key event.
   text_ += text;
 
@@ skipping 108 matching lines @@
   }
 
   // Whitelists Backspace key and arrow keys.
   std::vector<ui::KeyboardCode> whitelist_keycodes{
       ui::VKEY_BACK, ui::VKEY_LEFT, ui::VKEY_RIGHT, ui::VKEY_UP, ui::VKEY_DOWN};
   return std::find(whitelist_keycodes.begin(), whitelist_keycodes.end(),
                    ui_event->key_code()) != whitelist_keycodes.end();
 }
 
 }  // namespace input_method