Fix gn_helpers' parsing of bools.

build/gn_helpers_unittest.py

Index: build/gn_helpers_unittest.py
diff --git a/build/gn_helpers_unittest.py b/build/gn_helpers_unittest.py
index a493f6778ae24f2097d682ff1e01c8369d3972ac..72123f9359cd438089ae6d52f3be86fbbbded454 100644
--- a/build/gn_helpers_unittest.py
+++ b/build/gn_helpers_unittest.py
@@ -27,6 +27,13 @@ class UnitTest(unittest.TestCase):
       parser = gn_helpers.GNValueParser('123 456')
       parser.Parse()
 
+  def test_ParseBool(self):
+    parser = gn_helpers.GNValueParser('true')
+    self.assertEqual(parser.Parse(), True)
+
+    parser = gn_helpers.GNValueParser('false')
+    self.assertEqual(parser.Parse(), False)
+
   def test_ParseNumber(self):
     parser = gn_helpers.GNValueParser('123')
     self.assertEqual(parser.ParseNumber(), 123)