Build fix in chromium-libpac.

As of V8 r22703, static LowMemoryNotification API is no longer
supported.

See https://code.google.com/p/v8/source/detail?r=22703

Change-Id: I483de4004cfecc71b41ac6408e8ddad009c301e2
Merge "Build fix in chromium-libpac."