[turbofan] Redundant load elimination.

This is an initial version of redundant load elimination, currently
limited to LoadField operators, and implemented by walking the effect
chain.

TEST=unittests
R=svenpanne@chromium.org

Review URL: https://codereview.chromium.org/782473002

Cr-Commit-Position: refs/heads/master@{#25673}
Use merged JSTest config for performance tests.

The new config is now used for perf measurements. The old
ones are deleted to avoid redundancy.

This also ports https://codereview.chromium.org/754523004 to the new config file.

BUG=chromium:374740
LOG=n
TBR=ulan@chromium.org
NOTRY=true

Review URL: https://codereview.chromium.org/782673003

Cr-Commit-Position: refs/heads/master@{#25674}
Teach the test runner whether it's running on a trybot or not

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

Review URL: https://codereview.chromium.org/781763002

Cr-Commit-Position: refs/heads/master@{#25675}
[x86] Slow case of TruncateDoubleToI shouldn't be inline.

R=svenpanne@chromium.org

Review URL: https://codereview.chromium.org/778113002

Cr-Commit-Position: refs/heads/master@{#25676}