Run clang-modernize -use-nullptr over src/extensions/.

extensions/common/permissions/manifest_permission_set_unittest.cc

Index: extensions/common/permissions/manifest_permission_set_unittest.cc
diff --git a/extensions/common/permissions/manifest_permission_set_unittest.cc b/extensions/common/permissions/manifest_permission_set_unittest.cc
index ddac081fa159749f8307832ab18db9a756877ae1..9d0eb9505bda8dcd93aebfaa7b0a5e99981b790a 100644
--- a/extensions/common/permissions/manifest_permission_set_unittest.cc
+++ b/extensions/common/permissions/manifest_permission_set_unittest.cc
@@ -44,7 +44,7 @@ class MockManifestPermission : public ManifestPermission {
     const MockManifestPermission* other =
         static_cast<const MockManifestPermission*>(rhs);
     EXPECT_EQ(name_, other->name_);
-    return NULL;
+    return nullptr;
   }
 
   virtual ManifestPermission* Union(const ManifestPermission* rhs)