Version 4.2.77.18 (cherry-pick)

Merged 88e2d14c
Merged c96a2d3a

Initialize idle old generation allocation limit in constructor.

Use smaller heap growing factor in idle notification to start incremental marking when there is idle time >16ms.

BUG=478082,chromium:477323
LOG=N
R=rmcilory@chromium.org

Review URL: https://codereview.chromium.org/1100743003

Cr-Commit-Position: refs/branch-heads/4.2@{#21}
Cr-Branched-From: 3dfd929e-refs/heads/4.2.77@{#2}
Cr-Branched-From: e0110920-refs/heads/master@{#26757}