More assertion propagation.

- Added lookbehind propagation for the initial node; now, if the
  initial node is interested in what precedes it the automaton is
  given an initial all-consuming character class that determines it.
- Added verification of some node information invariants.  We now
  check that if a node expresses interest in what precedes it that
  information is available to it after assertion expansion.

[Lasse Reichstein, 2008-12-11 08:34:23]

LGTM

http://codereview.chromium.org/13343/diff/201/15
File src/jsregexp.cc (right):

http://codereview.chromium.org/13343/diff/201/15#newcode3677
Line 3677: bool has_been_expanded_;
Isn't this really two different visitors, rolled into one with a boolean tag?
How about making ValidateInfo pure virtual, and have two different subclasses
that implement ValidateInfo differently (as each branch of the conditional in
the current NodeValidator::ValidateInfo).

http://codereview.chromium.org/13343/diff/201/15#newcode3778
Line 3778: node = new TextNode(new RegExpCharacterClass('*'), node);
What happens if the look-behind is at the start of the string (there is no
character before the start position)? 
The current implementation preloads the previous character, or "\n" if at the
start of the string, so the code-generation can start out with a
current-character-test without reading. Will the code-generation be able to see
that this text node is the one before the real start?

http://codereview.chromium.org/13343/diff/201/19
File test/cctest/test-regexp.cc (right):

http://codereview.chromium.org/13343/diff/201/19#newcode1295
Line 1295: Execute("\\bboy\\b", false, true, true);
Could you (plural, everybody using this) not move this execution into another
file, so we don't get changes to this file that aren't really test related, or
meaningfull.
I'll write you a Perl script to compile and execute it if necessary.

[Christian Plesner Hansen, 2008-12-11 09:14:11]

http://codereview.chromium.org/13343/diff/201/15
File src/jsregexp.cc (right):

http://codereview.chromium.org/13343/diff/201/15#newcode3677
Line 3677: bool has_been_expanded_;
Good point.

http://codereview.chromium.org/13343/diff/201/15#newcode3778
Line 3778: node = new TextNode(new RegExpCharacterClass('*'), node);
Yes, it can use has_lookbehind to determine that.

http://codereview.chromium.org/13343/diff/201/19
File test/cctest/test-regexp.cc (right):

http://codereview.chromium.org/13343/diff/201/19#newcode1295
Line 1295: Execute("\\bboy\\b", false, true, true);
It's really convenient to be able to build this along with the rest of the code
through the build system and run it through the eclipse debugger.  If it's a
problem I can make sure to revert any changes I've made before committing.

Incidentally, meaningful has only one L.