The flag in question used to fall-back to Crankshaft whenever an OSR
request couldn't be handled by TurboFan. By now OSR in TurboFan is
sufficiently stabilized that one single --use-osr flag should do it.

R=titzer@chromium.org

Review-Url: https://codereview.chromium.org/1960043002
Cr-Commit-Position: refs/heads/master@{#36102}

AstGraphBuilder puts a constant context in from the beginning.
Also fix bug in merging contexts in environment.

R=mstarzinger@chromium.org
BUG=

Review URL: https://codereview.chromium.org/934293002

Cr-Commit-Position: refs/heads/master@{#26745}

R=mstarzinger@chromium.org
BUG=

Review URL: https://codereview.chromium.org/921083004

Cr-Commit-Position: refs/heads/master@{#26705}