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This fixes configuration of various targets (mostly adding some missing
files for is_android builds).

Adds a target setting up the content_shell_apk assets directory.

Uncomments the previously non-working dependencies from
libcontent_shell_content_view.

Adds forwarding of testonly in all of the android templates.

TBR=mark@

BUG=359249

Review URL: https://codereview.chromium.org/569923003

Cr-Commit-Position: refs/heads/master@{#296319}