Reason for revert:
Breaks nosnap: http://build.chromium.org/p/client.v8/builders/V8%20Linux%20-%20nosnap%20-%20debug%20-%202/builds/2407/steps/Check/logs/regress-4395
Original issue's description:
> [es6] Fix scoping for default parameters in arrow functions
>
> When eagerly parsing arrow functions, expressions in default
> parameter initializers are parsed in the enclosing scope,
> rather than in the function's scope (since that scope does not
> yet exist). This leads to VariableProxies being added to the
> wrong scope, and scope chains for FunctionLiterals being incorrect.
>
> This patch addresses these problems by adding a subclass of
> AstExpressionVisitor that moves VariableProxies to the proper
> scope and fixes up scope chains of FunctionLiterals.
>
> More work likely still needs to be done to make this work completely,
> but it's very close to correct.
>
> BUG=v8:4395
> LOG=y
>
> Committed: https://crrev.com/cf72aad39e51de9b7074ea039377c1812f4a2c6b
> Cr-Commit-Position: refs/heads/master@{#31402}
TBR=rossberg@chromium.org,caitpotter88@gmail.com,adamk@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=v8:4395
Review URL: https://codereview.chromium.org/1417463004
Cr-Commit-Position: refs/heads/master@{#31404}
e41614a058