Add "." accessors to GN.

Add "." accessors to GN.

Add support for values referring to a Scope, and add support for the dot operator to read such values out of a scope.

This is not currently used for anything. A followup patch will use this for the template implementation.

R=scottmg@chromium.org

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=259608

[brettw, 2014-03-24 16:58:27]

This just adds support for using the . operator, but doesn't actually hook it up
to the template yet.

[scottmg, 2014-03-25 05:04:22]

LGTM

https://codereview.chromium.org/207233003/diff/60001/tools/gn/parser.cc
File tools/gn/parser.cc (right):

https://codereview.chromium.org/207233003/diff/60001/tools/gn/parser.cc#newco...
tools/gn/parser.cc:22: PRECEDENCE_ASSIGNMENT = 1,  // Lowest prescedence.
no 's' in precedence

https://codereview.chromium.org/207233003/diff/60001/tools/gn/parser_unittest.cc
File tools/gn/parser_unittest.cc (right):

https://codereview.chromium.org/207233003/diff/60001/tools/gn/parser_unittest...
tools/gn/parser_unittest.cc:243: DoParserErrorTest("a = b.c.d", 1, 6);  // Can't
nest accessors (currently).
This one seems especially odd to not support, but I guess we don't need it for
templates, so meh.

[brettw, 2014-03-26 16:57:12]

Committed patchset #5 manually as r259608 (presubmit successful).