Remove HostDesktopType from BrowserList::GetInstance()

And make GetHostDesktopTypeForNativeView/Window and GetActiveDesktop()
no-ops.

R=sky@chromium.org
BUG=558054

Review URL: https://codereview.chromium.org/1637943003

Cr-Commit-Position: refs/heads/master@{#371938}
57 files changed