Arrow functions have been enabled by default since the 4.5 branch.

Review URL: https://codereview.chromium.org/1373633002

Cr-Commit-Position: refs/heads/master@{#31031}

Implements the strong mode proposal's static restrictions on the use of the
identifier 'undefined', for arrow functions. Assumes these restrictions are
intended to be identical to the restrictions on the use of 'eval and 'arguments'
in strict mode. In addition, Location variables inconsistantly named (e.g.
dupe_error_loc vs dupe_loc) are now consistently named the shorter way.

Baseline: https://codereview.chromium.org/1070633002

BUG=v8:3956
LOG=N

Review URL: https://codereview.chromium.org/1060883004

Cr-Commit-Position: refs/heads/master@{#27756}

identifier. Delete unused (and now incorrect) function IsValidStrictVariable.

Implements the strong mode proposal's static restrictions on the use of the
identifier 'undefined'. Assumes these restrictions are intended to be identical
to the restrictions on the use of 'eval' and 'arguments' in strict mode. The
AllowEvalOrArgumentsAsIdentifier enum has been renamed to
AllowRestrictedIdentifiers as logic involving it is now also used for this case.

BUG=v8:3956

LOG=N

Review URL: https://codereview.chromium.org/1070633002

Cr-Commit-Position: refs/heads/master@{#27744}