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

content/browser/device_orientation/provider.h

 // 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.
 
 #ifndef CONTENT_BROWSER_DEVICE_ORIENTATION_PROVIDER_H_
 #define CONTENT_BROWSER_DEVICE_ORIENTATION_PROVIDER_H_
 
 #include "base/memory/ref_counted.h"
 #include "content/browser/device_orientation/device_data.h"
 #include "content/common/content_export.h"
 
 namespace content {
 
 class CONTENT_EXPORT Provider : public base::RefCountedThreadSafe<Provider> {
  public:
   class Observer {
    public:
     // Called when device data changes.
     // An Observer must not synchronously call Provider::RemoveObserver
     // or Provider::AddObserver when this is called.
     virtual void OnDeviceDataUpdate(const DeviceData* device_data,
                                     DeviceData::Type device_data_type) = 0;
     DeviceData::Type device_data_type() { return device_data_type_; }
 
    protected:
-    Observer(DeviceData::Type device_data_type)
+    explicit Observer(DeviceData::Type device_data_type)
         : device_data_type_(device_data_type) {
     }
     virtual ~Observer() {}
 
    private:
     // Each Observer observes exactly one type of DeviceData.
     DeviceData::Type device_data_type_;
   };
 
   // Returns a pointer to the singleton instance of this class.
@@ skipping 21 matching lines @@
  private:
   friend class base::RefCountedThreadSafe<Provider>;
   static Provider* instance_;
 
   DISALLOW_COPY_AND_ASSIGN(Provider);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_BROWSER_DEVICE_ORIENTATION_PROVIDER_H_