[turbofan] add initial move optimizer

R=bmeurer@chromium.org

BUG=

Review URL: https://codereview.chromium.org/750813004

Cr-Commit-Position: refs/heads/master@{#25533}
Ensure double alignment when deserializing.

R=rmcilroy@chromium.org
BUG=chromium:436510
LOG=N
TEST=compile with V8_OOL_CONSTANT_POOL=1, run d8 with --verify-heap --test

Review URL: https://codereview.chromium.org/759823006

Cr-Commit-Position: refs/heads/master@{#25534}
Fast-to-slow migration should wipe out in-object space if it exists in the object after migration.

BUG=chromium:436816
LOG=N

Review URL: https://codereview.chromium.org/765473004

Cr-Commit-Position: refs/heads/master@{#25535}
Ship harmony-strings

R=rossberg@chromium.org, yangguo@chromium.org
LOG=Y

Review URL: https://codereview.chromium.org/761913002

Cr-Commit-Position: refs/heads/master@{#25536}
Add interceptor support for symbols

a revival of https://codereview.chromium.org/467013003

R=rossberg@chromium.org

BUG=

Review URL: https://codereview.chromium.org/760883002

Cr-Commit-Position: refs/heads/master@{#25537}
Add support for downloading clang

Still requires changes to gyp files to select the built-in clang as
compiler and make clang the default on the platforms we want it.

BUG=
R=dcarney@chromium.org,machenbach@chromium.org
LOG=n

Review URL: https://codereview.chromium.org/745963005

Cr-Commit-Position: refs/heads/master@{#25538}
Just print interesting idle notification events in --trace-idle-notification.

BUG=

Review URL: https://codereview.chromium.org/763063002

Cr-Commit-Position: refs/heads/master@{#25539}
Introduce a new growth criterion for the new space behind a flag

With this flag, we grow if more than 10% survived the last scavenge.

BUG=none
R=hpayer@chromium.org
LOG=n

Review URL: https://codereview.chromium.org/753543002

Cr-Commit-Position: refs/heads/master@{#25540}