Detect iOS simulator as an iOS test device.
Detect iOS simulator as an iOS test device.

If on a MacOS machine, iossim and Chromium.app are built than we can
launch and use them for running tests.

BUG=468565

Review URL: https://codereview.chromium.org/1015313002

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#321423}

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