[Chromecast] Set symbol_level=2 for Chromecast builds by default.
[Chromecast] Set symbol_level=2 for Chromecast builds by default.

Like official builds, Chromecast builds should enable full symbols by
default. This is useful for debugging engineering builds and those from
the field. Enable these by default so a GN arg need not be set
explicitly.

BUG= internal b/27602924

Review URL: https://codereview.chromium.org/1798093002

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#381066}

axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk