Change default download directory for Android Q

In Q, it is suggested that we use Context methods for accessing external
paths. https://developer.android.com/preview/privacy/scoped-storage
This change fixes a bug on Android Q where we don't have permission to store
downloaded pages.

Bug: 956679
Change-Id: If53b16c15204cdc396cf4ab1d84419b32c7384f1
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1627667
Commit-Queue: Dan H <harringtond@chromium.org>
Reviewed-by: Min Qin <qinmin@chromium.org>
Reviewed-by: Carlos Knippschild <carlosk@chromium.org>
Reviewed-by: Andrew Grieve <agrieve@chromium.org>
Cr-Commit-Position: refs/heads/master@{#663118}
2 files changed