Proof of concept: API for doing only one parsing pass instead of first preparsing and then parsing.

Proof of concept: API for doing only one parsing pass instead of first preparsing and then parsing.

It will read the data only once, and produce the same data preparsing used to
produce. The data can be saved in the cache if the upper layer wants so.

When Blink calls the preparsing API, it will always call the parsing API right
after. There's no reason why Parser couldn't produce it during the actual
parsing pass.

BUG=

[marja, 2014-02-27 10:55:44]

svenpanne@, wdyt about adding API for doing only one parsing pass (and producing
the same data that PreParser used to produce on the go)? Seems wasteful to do
two passes when we could get away with one. (Blink always parses right after it
has preparsed.)