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

base/threading/non_thread_safe_unittest.cc

Index: base/threading/non_thread_safe_unittest.cc
diff --git a/base/threading/non_thread_safe_unittest.cc b/base/threading/non_thread_safe_unittest.cc
index ee31701dc65ec6067d3c84702591040dc46acddb..8a82a637ab781f9e694ef5b23fd4c640b759d60e 100644
--- a/base/threading/non_thread_safe_unittest.cc
+++ b/base/threading/non_thread_safe_unittest.cc
@@ -47,7 +47,7 @@ class NonThreadSafeClass : public NonThreadSafe {
 // Calls NonThreadSafeClass::DoStuff on another thread.
 class CallDoStuffOnThread : public SimpleThread {
  public:
-  CallDoStuffOnThread(NonThreadSafeClass* non_thread_safe_class)
+  explicit CallDoStuffOnThread(NonThreadSafeClass* non_thread_safe_class)
       : SimpleThread("call_do_stuff_on_thread"),
         non_thread_safe_class_(non_thread_safe_class) {
   }
@@ -65,7 +65,8 @@ class CallDoStuffOnThread : public SimpleThread {
 // Deletes NonThreadSafeClass on a different thread.
 class DeleteNonThreadSafeClassOnThread : public SimpleThread {
  public:
-  DeleteNonThreadSafeClassOnThread(NonThreadSafeClass* non_thread_safe_class)
+  explicit DeleteNonThreadSafeClassOnThread(
+      NonThreadSafeClass* non_thread_safe_class)
       : SimpleThread("delete_non_thread_safe_class_on_thread"),
         non_thread_safe_class_(non_thread_safe_class) {
   }