[Media Router] Fix missing dependency.

https://chromium-review.googlesource.com/c/chromium/src/+/1985812 added
a generated include to chrome/ui/browser.h, which we can't depend on
directly for reasons.

This adds the dependency directly to fix the Open Screen try bots.

Bug: 1030821
Change-Id: Ic2b97bab07f57b8512097bcb2803c9cbc233f377
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2040735Reviewed-by: Yuri Wiitala <miu@chromium.org>
Commit-Queue: Yuri Wiitala <miu@chromium.org>
Commit-Queue: mark a. foltz <mfoltz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#738800}

chrome/browser/media/router/BUILD.gn

@@ -81,6 +81,7 @@ static_library("router") {
       # resolution for browser.h, which is used in multiple extension-only
       # files.
       # TODO(crbug.com/1030821): Resolve circular dependencies
+      "//components/paint_preview/buildflags",
       "//components/signin/public/base:signin_buildflags",
       "//components/translate/content/common",
       "//mojo/public/cpp/bindings",