This patch implements the runtime semantics of static public
class fields.

Adds a new InitializeClassFieldsStatement AST node that contains
all the static class fields and their initializers. 

ClassLiteral is now desugared to be included in a do-exp that calls 
an initializer function which contains this new AST node.

Bug: v8:5367
Change-Id: I3574e4c685f1c039de42521c122e24f8d28e5d6c
Reviewed-on: https://chromium-review.googlesource.com/714817Reviewed-by: Adam Klein <adamk@chromium.org>
Reviewed-by: Ross McIlroy <rmcilroy@chromium.org>
Reviewed-by: Mythri Alle <mythria@chromium.org>
Commit-Queue: Sathya Gunasekaran <gsathya@chromium.org>
Cr-Commit-Position: refs/heads/master@{#48835}