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 f81b316aa2e025c261369e86d4ed32d106236493..760d70bfbf731884c4ef4a59e8079f656c06a148 100755
--- a/PRESUBMIT_test.py
+++ b/PRESUBMIT_test.py
@@ -413,6 +413,52 @@ class InvalidOSMacroNamesTest(unittest.TestCase):
     self.assertEqual(0, len(errors))
 
 
+class CheckContradictoryNotreachedUseTest(unittest.TestCase):
+  def testValid(self):
+    lines = ['{',
+             '  // NOTREACHED();',
+             '  /* NOTREACHED(); */',
+             "  char a = '\\\\', b = '\\0', c = '\\'';",
+             '  char d[] = "NOTREACHED();";',
+             '  NOTREACHED(); // blah',
+             '  /* comment */',
+             '  // line continuation \\',
+             '  still inside comment',
+             '  // comment followed by empty line',
+             '',
+             '  ;; ; ;;;',
+             '}',
+             'switch (i) {',
+             '  case 7: NOTREACHED(); break;',
+             '}']
+    output = PRESUBMIT._CheckContradictoryNotreachedUseInFile(
+        MockInputApi(), MockFile('some/path/foo_platform.cc', lines))
+    self.assertEqual(0, len(output))
+
+  def testInvalid(self):
+    lines = ['{',
+             '  NOTREACHED();',
+             '  return;',
+             '}',
+             '{',
+             '  NOTREACHED();',
+             '  /* */',
+             '  return;',
+             '  /* */',
+             '}',
+             '{',
+             '  NOTREACHED();',
+             '  // trailing space, not a line continuation \\ ',
+             '  return;',
+             '}',
+             'switch (i) {',
+             '  case 7: NOTREACHED(); some_thing(); break;',
+             '}']
+    output = PRESUBMIT._CheckContradictoryNotreachedUseInFile(
+        MockInputApi(), MockFile('some/path/foo_platform.cc', lines))
+    self.assertEqual(4, len(output))
+
+
 class CheckAddedDepsHaveTetsApprovalsTest(unittest.TestCase):
   def testFilesToCheckForIncomingDeps(self):
     changed_lines = [