Include <vector> in fake_desktop_environment.h
Include <vector> in fake_desktop_environment.h

fake_desktop_environment.h uses std::vector<> but wasn't including
<vector>.

Review URL: https://codereview.chromium.org/1906263002

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#388970}

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