chromium: multiple issues

• CVE-2015-1209 (use-after-free)

Use-after-free in DOM, possibly leading to arbitrary code execution.
Credit to Maksymillian Motyl.

• CVE-2015-1210 (cross-origin bypass)

Cross-origin-bypass in V8 bindings allows an attacker to bypass the
same-origin policy.

• CVE-2015-1211 (privilege escalation)

Privilege escalation using service workers.

• CVE-2015-1212

Various fixes from internal audits, fuzzing and other initiatives,
fixing unspecified vulnerabilities not disclosed by upstream.