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

base/synchronization/lock_unittest.cc

Index: base/synchronization/lock_unittest.cc
diff --git a/base/synchronization/lock_unittest.cc b/base/synchronization/lock_unittest.cc
index a048f8570c2eb455ee9b9f56c39e0a7e43eeeb16..e87571d0d85b164b9afdabad93d8eddb6ba92a5a 100644
--- a/base/synchronization/lock_unittest.cc
+++ b/base/synchronization/lock_unittest.cc
@@ -16,7 +16,7 @@ namespace base {
 
 class BasicLockTestThread : public PlatformThread::Delegate {
  public:
-  BasicLockTestThread(Lock* lock) : lock_(lock), acquired_(0) {}
+  explicit BasicLockTestThread(Lock* lock) : lock_(lock), acquired_(0) {}
 
   virtual void ThreadMain() OVERRIDE {
     for (int i = 0; i < 10; i++) {
@@ -91,7 +91,7 @@ TEST(LockTest, Basic) {
 
 class TryLockTestThread : public PlatformThread::Delegate {
  public:
-  TryLockTestThread(Lock* lock) : lock_(lock), got_lock_(false) {}
+  explicit TryLockTestThread(Lock* lock) : lock_(lock), got_lock_(false) {}
 
   virtual void ThreadMain() OVERRIDE {
     got_lock_ = lock_->Try();