Revert "Forward declaration for Isolate / Platform in libplatform.h." and "Fixes d8 on windows following.".

This reverts commit 0f57ce8f1a3d6b4f3a4b65739d719b8467ff5d9c.
and 3245b8cb832f4a948aff9fb1c271cc08c4690d3b for breaking Chromium
compile.

TBR=machenbach@chromium.org

Review URL: https://codereview.chromium.org/743533003

Cr-Commit-Position: refs/heads/master@{#25411}
[turbofan] Smartify typing of NumberToInt32 and NumberToUint32.

According to ES5 9.5 and 9.6, NaN, -inf, +inf, -0 and 0 all truncate to
zero for both ToInt32 and ToUint32, so we can be a lot smarter in the
typer, loosing less information upon truncation (i.e. x | 0 and x >>> 0).

R=jarin@chromium.org

Review URL: https://codereview.chromium.org/739743003

Cr-Commit-Position: refs/heads/master@{#25412}
fix typo in pipeline.cc

TBR=bmeurer@chromium.org

BUG=

Review URL: https://codereview.chromium.org/743603003

Cr-Commit-Position: refs/heads/master@{#25413}