IDL parser: fix rebuilding of (stale) cached parser tables

IDL parser: fix rebuilding of (stale) cached parser tables

The yacc parser's tables are cached to improve build performance, and are
rebuilt by running blink_idl_parser.py directly, which simply initializes
the IDL parser and expects PLY (yacc.py) to write the cached tables as a
side-effect.

However, if the file containing the cached tables exists, then PLY will
instead try to load the stale cache. If that succeeds, it will disable
the rewriting, since there's no point in writing to the cache what was
just read from it.

Fix by always deleting the cache file whenever blink_idl_parser.py is
executed directly, before initializing the parser. This way, PLY will not
use cached tables, and will instead write the cache file.

BUG=387631
Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=176745

[Jens Widell, 2014-06-23 10:35:17]

Please review.

I believe this fixes the weirdness discussed in
https://codereview.chromium.org/329163002/.

[haraken, 2014-06-23 10:47:18]

LGTM, but Nils wants to confirm.

[Nils Barth (inactive), 2014-06-23 11:05:14]

LGTM, with one comment request.

Great sleuthing!
PLY internals are pretty subtle; thanks for figuring this out!

https://codereview.chromium.org/332683004/diff/1/Source/bindings/scripts/blin...
File Source/bindings/scripts/blink_idl_parser.py (right):

https://codereview.chromium.org/332683004/diff/1/Source/bindings/scripts/blin...
Source/bindings/scripts/blink_idl_parser.py:449: parser =
BlinkIDLParser(outputdir=outputdir, rewrite_tables=True)
Could you add a comment here explaining why this is necessary?
(Prevents using stale files.)

[Jens Widell, 2014-06-23 11:20:23]

The CQ bit was checked by jl@opera.com

[commit-bot: I haz the power, 2014-06-23 11:20:35]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/jl@opera.com/332683004/20001

[commit-bot: I haz the power, 2014-06-23 12:25:11]

Change committed as 176745