Mozc cannot be activated in the search box on the task bar when configured to be the default IME on Windows 10

[yukawa]

Environment

• Mozc 2.17.2288.100
• Microsoft Windows 10 1511 (OS Build 10586.36)

Steps to reproduce

1. Build Mozc 2.17.2288.102 for Windows.
2. Install Mozc into Windows 10.
3. Make sure that Mozc is the default input method.
4. Sign out.
5. Sign in.
6. Launch nodepad application. Make sure that you can use Mozc there.
7. Focus in the search box on the task bar.
8. Try to turn on IME.

Expected behavior

• After step 8, Mozc can be enabled and you can type Japanese text.

Actual behavior

• After step 8, Mozc can never be enabled thus you are not able to type Japanese text.

Additional information

Internal Issue ID: 24793812.