Function declarations were previously permitted by V8 in many locations
which no ECMAScript specification allowed; the ECMAScript 2015 spec
enumerates a few locations (in blocks, as well as after labels and in
conditionals when in sloppy mode). This patch ships the flag to restrict
the usage of function declarations to those contexts.

R=adamk
LOG=Y
BUG=v8:4824
CQ_INCLUDE_TRYBOTS=tryserver.chromium.linux:linux_chromium_rel_ng;tryserver.blink:linux_blink_rel

Review URL: https://codereview.chromium.org/1799233003

Cr-Commit-Position: refs/heads/master@{#34828}

R=jkummerow@chromium.org

Review URL: https://codereview.chromium.org/18068003

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@15370 ce2b1a6d-e550-0410-aec6-3dcde31c8c00