Certain token combinations (e.g. number literal followed by semicolon) will
result in a single AST node, but require many levels of recursive descent
parsing to determine this (11 in this example). For some 'obvious'
combinations, we'll simply generate the appropriate AST node fairly far up
in the call tree.

This yields a mild but consistent parser speedup. The main con is code duplication.

[Speedup between 0..20ms in parse time among a set of 25 commonly used sites. Speedup of ~180ms for a site w/ a very large codebase (adwords.google.com). Minor slow-downs between 0..8ms for <20% of sites.]

R=marja@chromium.org
BUG=v8:4947

Review-Url: https://codereview.chromium.org/2188153002
Cr-Commit-Position: refs/heads/master@{#38591}