Don't use ConsStringIterator to compute string hashes

R=yangguo@chromium.org

BUG=

Review URL: https://codereview.chromium.org/762773002

Cr-Commit-Position: refs/heads/master@{#25518}
Introduce legacy const slots in correct context.

R=rossberg@chromium.org
BUG=chromium:410030
LOG=Y

Review URL: https://codereview.chromium.org/756293004

Cr-Commit-Position: refs/heads/master@{#25519}
Stage ES6 block scoping.

R=rossberg@chromium.org
BUG=v8:2198
LOG=Y

Review URL: https://codereview.chromium.org/751503004

Cr-Commit-Position: refs/heads/master@{#25520}
[turbofan] Implement jump threading after register allocation.

R=dcarney@chromium.org
BUG=

Review URL: https://codereview.chromium.org/754843002

Cr-Commit-Position: refs/heads/master@{#25521}
Fix Windows 32.

TBR=dcarney@chromium.org
BUG=

Review URL: https://codereview.chromium.org/755323007

Cr-Commit-Position: refs/heads/master@{#25522}
Some micro-optimizations in the scheduler.

R=bmeurer@chromium.org

Review URL: https://codereview.chromium.org/764533003

Cr-Commit-Position: refs/heads/master@{#25523}
Make GCTracer not reentrant.

BUG=

Review URL: https://codereview.chromium.org/754023003

Cr-Commit-Position: refs/heads/master@{#25524}
Reuse CFGBuilder in the scheduler to save memory.

R=bmeurer@chromium.org

Review URL: https://codereview.chromium.org/755353003

Cr-Commit-Position: refs/heads/master@{#25525}