We need a test case for the behavior that:

When disabling the spellcheck feature (via context menu or settings), all spelling markers in all frames should be removed.

Now that the marker removal logic has been moved to components/spellcheck/renderer/spellcheck.cc, we need a new test case for this behavior.

Basic idea:

1. Start a renderer process with a mock browser

2. Add mock SpellCheckHost or SpellCheckMessageFilter to the mock browser, depending on the platform, so that the renderer can get spellcheck results

3. Load some HTML, trigger spellchecker, and wait until marker appears

4. Call SpellCheck::Initialize() with enable=false, to mock the user preference change that spellcheck is disabled

5. Assert that all spelling markers are removed