Fix newly discovered presubmit errors.

src/effects.h

 // Copyright 2013 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef V8_EFFECTS_H_
 #define V8_EFFECTS_H_
 
 #include "src/v8.h"
 
 #include "src/types.h"
@@ skipping 15 matching lines @@
 // merges into a previous effect, i.e., type bounds are merged. Alternative
 // composition always merges bounds. It yields a possible effect if at least
 // one was only possible.
 struct Effect {
   enum Modality { POSSIBLE, DEFINITE };
 
   Modality modality;
   Bounds bounds;
 
   Effect() : modality(DEFINITE) {}
-  Effect(Bounds b, Modality m = DEFINITE) : modality(m), bounds(b) {}
+  explicit Effect(Bounds b, Modality m = DEFINITE) : modality(m), bounds(b) {}
 
   // The unknown effect.
   static Effect Unknown(Zone* zone) {
     return Effect(Bounds::Unbounded(zone), POSSIBLE);
   }
 
   static Effect Forget(Zone* zone) {
     return Effect(Bounds::Unbounded(zone), DEFINITE);
   }
 
@@ skipping 280 matching lines @@
     NestedEffects result = *this;
     result.pop();
     DCHECK(!this->is_empty());
     return result;
   }
 };
 
 } }  // namespace v8::internal
 
 #endif  // V8_EFFECTS_H_