Clean up node iteration

- Create a first-class Edge type.
- Separate node and edge iterators
- Make iterators only responsible for iteration
- Make it possible to modify the use edge iterator while iterating.
- Add the ability to update inputs to Edges directly.

Review URL: https://codereview.chromium.org/765983002

Cr-Commit-Position: refs/heads/master@{#25616}
Stage ES6 classes and object literal extensions.

R=arv@chromium.org,rossberg@chromium.org
BUG=v8:3330
LOG=Y

Review URL: https://codereview.chromium.org/774653002

Cr-Commit-Position: refs/heads/master@{#25617}
Trace how long it takes to compute the weak closure during mark-compact

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

Review URL: https://codereview.chromium.org/769253002

Cr-Commit-Position: refs/heads/master@{#25618}
[ia32] Introduce FMA3 instructions on scalar data elements.

port 83a635e0d70f144300ea83be0d7effc1eb1bf6ef

BUG=

Review URL: https://codereview.chromium.org/773783002

Cr-Commit-Position: refs/heads/master@{#25619}
Make generic algorithm a little less generic.

R=titzer@chromium.org

Review URL: https://codereview.chromium.org/760493003

Cr-Commit-Position: refs/heads/master@{#25620}
Restrict floating control to minimal control-connected component.

R=jarin@chromium.org
TEST=cctest/test-scheduler/NestedFloatingDiamondWithChain

Review URL: https://codereview.chromium.org/738613005

Cr-Commit-Position: refs/heads/master@{#25621}