Put newspace evacuation in an EvacuationScope (Chromium issue 471554).

Fix libdl dependency on Android and remove librt hack (Chromium issue 469973).

Ensure that GC idle notifications either make progress or stop requesting more GCs (Chromium issue 470615).

Layout descriptor must be trimmed when corresponding descriptors array is trimmed to stay in sync (Chromium issue 470804).

Fix JSON parser Handle leak (issue 3976).

Performance and stability improvements on all platforms.

Cr-Commit-Position: refs/heads/4.3.62@{#1}
Cr-Branched-From: 21241680ae6e8dd51ad018df85281f67c367a0f3-refs/heads/master@{#27544}