To make desktopCapture autotest in chromium more meaningful, it's better to creake fake capturer of each capture type. Here we can reuse the FakeDesktopCapturer for window capture in chromium. Bug: chromium:699201 Change-Id: Icbe134d99cbd4980bf27fe74c1c629a1469836ea Reviewed-on: https://webrtc-review.googlesource.com/26360 Reviewed-by: Zijie He <zijiehe@chromium.org> Commit-Queue: Brave Yao <braveyao@webrtc.org> Cr-Commit-Position: refs/heads/master@{#20901}