When building in the Chromium tree, chromium_code is necessary to apply
Chromium’s build/filename_rules.gypi. Crashpad’s build depends on these
rules. chromium_code also enables a high warning level, which is
desirable for Crashpad.
BUG=crashpad:12
R=rsesek@chromium.org
Review URL: https://codereview.chromium.org/986873002
