I realized it can be removed.
OnTextInputTypeChanged is only utilized by TextInputTestHelper, but it can use OnTextInputStateChanged instead.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/878de580c1c74bafbbd1d3045075b6d13fbdd4f1

commit 878de580c1c74bafbbd1d3045075b6d13fbdd4f1
Author: oka@chromium.org <oka@chromium.org>
Date: Thu Jul 13 03:45:13 2017

Remove OnTextInputTypeChanged, which is only called by mock.

Bug:  739988 
Change-Id: Ic484a862e25700611581989f6e660267a01a2cbe
Reviewed-on: https://chromium-review.googlesource.com/562844
Commit-Queue: Keigo Oka <oka@chromium.org>
Reviewed-by: Shu Chen <shuchen@chromium.org>
Reviewed-by: Jochen Eisinger <jochen@chromium.org>
Cr-Commit-Position: refs/heads/master@{#486261}
[modify] https://crrev.com/878de580c1c74bafbbd1d3045075b6d13fbdd4f1/ash/magnifier/magnification_controller.cc
[modify] https://crrev.com/878de580c1c74bafbbd1d3045075b6d13fbdd4f1/chrome/browser/chromeos/accessibility/accessibility_highlight_manager.h
[modify] https://crrev.com/878de580c1c74bafbbd1d3045075b6d13fbdd4f1/chrome/browser/chromeos/input_method/textinput_test_helper.cc
[modify] https://crrev.com/878de580c1c74bafbbd1d3045075b6d13fbdd4f1/chrome/browser/chromeos/input_method/textinput_test_helper.h
[modify] https://crrev.com/878de580c1c74bafbbd1d3045075b6d13fbdd4f1/content/public/test/text_input_test_utils.cc
[modify] https://crrev.com/878de580c1c74bafbbd1d3045075b6d13fbdd4f1/content/public/test/text_input_test_utils.h
[modify] https://crrev.com/878de580c1c74bafbbd1d3045075b6d13fbdd4f1/ui/base/ime/input_method_base_unittest.cc
[modify] https://crrev.com/878de580c1c74bafbbd1d3045075b6d13fbdd4f1/ui/base/ime/input_method_observer.h
[modify] https://crrev.com/878de580c1c74bafbbd1d3045075b6d13fbdd4f1/ui/base/ime/mock_input_method.cc
[modify] https://crrev.com/878de580c1c74bafbbd1d3045075b6d13fbdd4f1/ui/keyboard/keyboard_controller.h
[modify] https://crrev.com/878de580c1c74bafbbd1d3045075b6d13fbdd4f1/ui/views/win/hwnd_message_handler.cc
[modify] https://crrev.com/878de580c1c74bafbbd1d3045075b6d13fbdd4f1/ui/views/win/hwnd_message_handler.h