wm/views: makes objects using Env take Env

This allows for multiple Envs at the same time. Additionally:
. NativeWidgetPrivate::CreateNativeWidget: now takes InitParams
. NativeWidgetPrivate::IsMouseButtonDown() is now an member function.

BUG=847992
TEST=covered by tests

Change-Id: Ic35b274c0a927a7c602809a7e611383b5d3dd3e2
Reviewed-on: https://chromium-review.googlesource.com/1166148
Commit-Queue: Scott Violet <sky@chromium.org>
Reviewed-by: Michael Wasserman <msw@chromium.org>
Cr-Commit-Position: refs/heads/master@{#581621}
20 files changed