Move ScopeInfo allocation out of DeclarationScope::Analyse and do it later
in the compile when finalizing unoptimized code generation. This is to enable
scope analysis to be done without heap allocation so it could run off-thread.

BUG=v8:5203

Change-Id: I954aacd4353925bbbd5a940d979027de2c52e1fd
Reviewed-on: https://chromium-review.googlesource.com/581108Reviewed-by: Yang Guo <yangguo@chromium.org>
Reviewed-by: Michael Starzinger <mstarzinger@chromium.org>
Commit-Queue: Ross McIlroy <rmcilroy@chromium.org>
Cr-Commit-Position: refs/heads/master@{#46862}