Add InputMethodObserver support into InputMethodBase

This is a preparation CL to fix issue 164964.

Following observer callbacks are defined but not yet
supported by ui::InputMethodBase and its sub classes.
- InputMethodObserver::OnCaretBoundsChanged
- InputMethodObserver::OnInputLocaleChanged

This CL makes these callbacks functional for each
sub class of ui::InputMethodBase.

BUG=164964
TEST=ui_unittests --gtest_filter=InputMethodBaseTest.*

Review URL: https://codereview.chromium.org/48393003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@231563 0039d316-1c4b-4281-b951-d872f2087c98
void InputMethodLinuxX11::OnCaretBoundsChanged(
void InputMethodLinuxX11::OnCaretBoundsChanged(const TextInputClient* client) {
  if (IsTextInputClientFocused(client)) {
    input_method_context_->OnCaretBoundsChanged(
        GetTextInputClient()->GetCaretBounds());
  }
  InputMethodBase::OnCaretBoundsChanged(client);
 }

void InputMethodLinuxX11::OnCaretBoundsChanged(
    const TextInputClient* client) {
  if (!IsTextInputClientFocused(client))
    return;
  input_method_context_->OnCaretBoundsChanged(
      GetTextInputClient()->GetCaretBounds());
 }
