Use Context from WindowAndroid in ScreenCapture

This is so we can get the correct e.g. DPI. In a follow up CL, we should
update the DPI etc if the tab is reparented (new WindowAndroid), or if
it's moved to a different screen (context updates).

Bug: 352187279
Test: CQ
Change-Id: I9db1e48bd126ca9f0da725c4cc2669716bb70695
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6627334
Commit-Queue: Eliot Courtney <edcourtney@chromium.org>
Reviewed-by: Calder Kitagawa <ckitagawa@chromium.org>
Reviewed-by: David Trainor <dtrainor@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1476340}