Add the url optional argument to adb_gdb --start.
Add the url optional argument to adb_gdb --start.

Allow the start option to specify an optional argument of <url> to be
started.

BUG=597325

Review URL: https://codereview.chromium.org/1825933002

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#384167}

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