Some extensions to Expression

Added code to conservatively figure out what a typeof <the expression>
would yield, and conservative folding.  These help with static
analysis and code optimization.

And added a static utility method
  Operation.is(ParseTreeNode, Operator)
to replace a frequently appearing but hard to read idiom.


Submitted @3825

[metaweta, 2009-10-22 01:26:58]

LGTM modulo the one extra test

http://codereview.appspot.com/135053/diff/1002/46
File tests/com/google/caja/parser/js/ExpressionTest.java (right):

http://codereview.appspot.com/135053/diff/1002/46#newcode143
Line 143: }
Test a floating point expression like -1.5 or 6.02e+23 for 'number'.

http://codereview.appspot.com/135053/diff/1002/46#newcode150
Line 150: assertFolded("'13'", "'1' + '3'");
dupe

[MikeSamuel, 2009-10-22 01:42:03]

http://codereview.appspot.com/135053/diff/1002/46
File tests/com/google/caja/parser/js/ExpressionTest.java (right):

http://codereview.appspot.com/135053/diff/1002/46#newcode143
Line 143: }
On 2009/10/22 01:26:58, metaweta wrote:
> Test a floating point expression like -1.5 or 6.02e+23 for 'number'.

Done.

http://codereview.appspot.com/135053/diff/1002/46#newcode150
Line 150: assertFolded("'13'", "'1' + '3'");
On 2009/10/22 01:26:58, metaweta wrote:
> dupe

Done.

[metaweta, 2009-10-22 05:27:11]

lgtm