Avoid temporary Vectors for arrow function parameter lists

Avoid temporary Vectors for arrow function parameter lists

Instead of using a Collector to gather the parameters from parameter
lists of arrow functions and then calling Collector::ToVector() on it,
declare the parameters on the function Scope as the AST subtree with
the paramters is traversed. This avoids the memory allocations done
by Collector, and removed the chance of leaking the result obtained
from Collector::ToVector().

BUG=

[aperez, 2014-07-10 19:32:34]

Apart from avoiding temporary allocations, this should avoid the ASAN
bot failures!

[marja, 2014-07-11 07:01:14]

Sorry, I saw this after I had already reverted the CL. Can you create a new
whole one with the fix?

[aperez, 2014-07-11 09:35:20]

On 2014/07/11 at 07:01:14, marja wrote:
> Sorry, I saw this after I had already reverted the CL. Can you create a new
whole one with the fix?

Sure thing.