Start immediate dominator propagation at entry to floating control.

R=titzer@chromium.org

Review URL: https://codereview.chromium.org/761673004

Cr-Commit-Position: refs/heads/master@{#25543}
Just finalize incremental marking when marking is done in idle notification.

BUG=

Review URL: https://codereview.chromium.org/733893003

Cr-Commit-Position: refs/heads/master@{#25544}
Re-land: Distinguish beween final incremental mark-compact and full mark-compact event in IdleNotification.

BUG=
R=ulan@chromium.org

Review URL: https://codereview.chromium.org/765743002

Cr-Commit-Position: refs/heads/master@{#25545}
Just account for context disposal garbage collections in context disposal stats counters.

BUG=

Review URL: https://codereview.chromium.org/765773002

Cr-Commit-Position: refs/heads/master@{#25546}
Fix reduction result for branches in generic lowering.

R=bmeurer@chromium.org

Review URL: https://codereview.chromium.org/750333003

Cr-Commit-Position: refs/heads/master@{#25547}
Remove deprecated constant helpers from JSGenericLowering.

R=bmeurer@chromium.org

Review URL: https://codereview.chromium.org/761143002

Cr-Commit-Position: refs/heads/master@{#25548}