This patch moves the method ParseFunctionDeclaration to ParserBase.
It also cleans up some forgotten method headers in parser and preparser.

R=adamk@chromium.org, verwaest@chromium.org
BUG=
LOG=N

Review-Url: https://codereview.chromium.org/2376293002
Cr-Commit-Position: refs/heads/master@{#39901}