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

chrome/browser/download/download_path_reservation_tracker_unittest.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "base/file_path.h"
 #include "base/file_util.h"
 #include "base/files/scoped_temp_dir.h"
 #include "base/memory/weak_ptr.h"
 #include "base/message_loop.h"
 #include "base/observer_list.h"
@@ skipping 12 matching lines @@
 using testing::AnyNumber;
 using testing::Return;
 using testing::ReturnRef;
 using testing::ReturnRefOfCopy;
 
 namespace {
 
 // MockDownloadItem with real observers and state.
 class FakeDownloadItem : public MockDownloadItem {
  public:
-  explicit FakeDownloadItem()
+  FakeDownloadItem()
       : state_(IN_PROGRESS) {
   }
   virtual ~FakeDownloadItem() {
     FOR_EACH_OBSERVER(Observer, observers_, OnDownloadDestroyed(this));
     EXPECT_EQ(0u, observers_.size());
   }
   virtual void AddObserver(Observer* observer) OVERRIDE {
     observers_.AddObserver(observer);
   }
   virtual void RemoveObserver(Observer* observer) OVERRIDE {
@@ skipping 373 matching lines @@
   item->UpdateObservers();
   message_loop_.RunUntilIdle();
   EXPECT_FALSE(IsPathInUse(path));
   EXPECT_TRUE(IsPathInUse(new_target_path));
 
   // Destroying the item should release the reservation.
   item.reset();
   message_loop_.RunUntilIdle();
   EXPECT_FALSE(IsPathInUse(new_target_path));
 }