Add PRESUBMIT.py warning for contradictory NOTREACHED() use.

PRESUBMIT_test.py

Index: PRESUBMIT_test.py
diff --git a/PRESUBMIT_test.py b/PRESUBMIT_test.py
index 3bebc678c616978a8494da5cee552004cc2b90a7..baa5f88741d9c2727f2846264dbb95448572cf5f 100755
--- a/PRESUBMIT_test.py
+++ b/PRESUBMIT_test.py
@@ -393,6 +393,44 @@ class InvalidOSMacroNamesTest(unittest.TestCase):
     self.assertEqual(0, len(errors))
 
 
+class CheckContradictoryNotreachedUseTest(unittest.TestCase):
+  def testValid(self):
+    lines = [r'{',
+             r"  char a = '\\', b = '\0', c = '\'';",
+             r'  char d[] = "NOTREACHED();";',
+             r'  NOTREACHED(); // NOTREACHED();',
+             r'  /* NOTREACHED(); */',
+             r'  // line continuation \\',
+             r'  still inside comment',
+             r'  // comment followed by empty line',
+             r'',
+             r'}',
+             r'switch (i) {',
+             r'  case 7: NOTREACHED(); break;',
+             r'}']
+    output = PRESUBMIT._CheckContradictoryNotreachedUseInFile(
+        MockInputApi(), MockFile('some/path/foo_platform.cc', lines))
+    self.assertEqual(0, len(output))
+
+  def testInvalid(self):
+    lines = ['{',
+             '  NOTREACHED();',
+             '  return;',
+             '}',
+             '{',
+             '  NOTREACHED();',
+             '  /* */',
+             '  return;',
+             '  /* */',
+             '}',
+             'switch (i) {',
+             '  case 7: NOTREACHED(); some_thing(); break;',
+             '}']
+    output = PRESUBMIT._CheckContradictoryNotreachedUseInFile(
+        MockInputApi(), MockFile('some/path/foo_platform.cc', lines))
+    self.assertEqual(3, len(output))
+
+
 class CheckAddedDepsHaveTetsApprovalsTest(unittest.TestCase):
   def testFilesToCheckForIncomingDeps(self):
     changed_lines = [