ExecutableAccessorInfo::clear_setter should set a null foreign pointer

R=jkummerow@chromium.org
BUG=433458
LOG=N

Review URL: https://codereview.chromium.org/759683004

Cr-Commit-Position: refs/heads/master@{#25737}
Reland 'Do not embed constant functions in StoreTransition stub.'

BUG=v8:3629
LOG=N

Review URL: https://codereview.chromium.org/787153002

Cr-Commit-Position: refs/heads/master@{#25738}
Reland remaining parts of 'Use weak cells in map checks in polymorphic ICs'

BUG=v8:3663
LOG=N

Review URL: https://codereview.chromium.org/792543003

Cr-Commit-Position: refs/heads/master@{#25739}
Reland "[turbofan] Fix control reducer bug with NTLs."

R=mstarzinger@chromium.org
BUG=

Review URL: https://codereview.chromium.org/789083004

Cr-Commit-Position: refs/heads/master@{#25740}
Reland "Use same blob format for internal and external snapshots."

Review URL: https://codereview.chromium.org/791723004

Cr-Commit-Position: refs/heads/master@{#25741}
[turbofan] update register allocator with auto, nullptr and ZoneVector

BUG=

Review URL: https://codereview.chromium.org/789083005

Cr-Commit-Position: refs/heads/master@{#25742}
[turbofan] Fix cycles introduced by pushing ToNumbers into phis.

TEST=cctest
R=mstarzinger@chromium.org

Review URL: https://codereview.chromium.org/790123002

Cr-Commit-Position: refs/heads/master@{#25743}