Add missing (and remove superfluous) 'explicit' from constructors.

content/public/test/test_navigation_observer.h

Index: content/public/test/test_navigation_observer.h
diff --git a/content/public/test/test_navigation_observer.h b/content/public/test/test_navigation_observer.h
index 70cda33b4f4869731cec546632e2b3b28dfcec6c..fe4885654ce41676f743624727edf5fae763cba5 100644
--- a/content/public/test/test_navigation_observer.h
+++ b/content/public/test/test_navigation_observer.h
@@ -47,9 +47,8 @@ class TestNavigationObserver : public NotificationObserver {
   // Note: |js_injection_ready_observer| is owned by the caller and should be
   // valid until this class is destroyed. Subclasses using this constructor MUST
   // call RegisterAsObserver when a NavigationController becomes available.
-  explicit TestNavigationObserver(
-      JsInjectionReadyObserver* js_injection_ready_observer,
-      int number_of_navigations);
+  TestNavigationObserver(JsInjectionReadyObserver* js_injection_ready_observer,
+                         int number_of_navigations);
 
   // Register this TestNavigationObserver as an observer of the |source|.
   void RegisterAsObserver(const NotificationSource& source);