Add <if> blocks to xtb files in the simplest possible way. This currently

Add <if> blocks to xtb files in the simplest possible way.  This currently
only supports checking the OS, but we can add more information if
necessary.

BUG=16884

[tony, 2009-07-21 20:34:06]

There's an example of the syntax in patchset 1.  It's pretty much the same as
the grd files.

I tried to share code with the grd file parser, but they're pretty far apart so
I just went with the simplest thing.

[Evan Martin, 2009-07-22 00:29:54]

LGTM

http://codereview.chromium.org/159148/diff/6/1001
File tools/grit/grit/xtb_reader.py (right):

http://codereview.chromium.org/159148/diff/6/1001#newcode46
Line 46: assert self.if_expr is None
Is there some way to pass a string to "assert" so if someone catches this
they'll get a useful error message?

http://codereview.chromium.org/159148/diff/6/1001#newcode52
Line 52: if_result = True
Might be clearer with a name like "should run callback", since it's also used in
the case where there's no "if" block.

[tony, 2009-07-22 00:37:21]

http://codereview.chromium.org/159148/diff/6/1001
File tools/grit/grit/xtb_reader.py (right):

http://codereview.chromium.org/159148/diff/6/1001#newcode46
Line 46: assert self.if_expr is None
On 2009/07/22 00:29:55, Evan Martin wrote:
> Is there some way to pass a string to "assert" so if someone catches this
> they'll get a useful error message?

Done.

http://codereview.chromium.org/159148/diff/6/1001#newcode52
Line 52: if_result = True
On 2009/07/22 00:29:55, Evan Martin wrote:
> Might be clearer with a name like "should run callback", since it's also used
in
> the case where there's no "if" block.

Done.