(Second attempt at http://codereview.chromium.org/553069/show)...

chrome/browser/geolocation/empty_device_data_provider.h

+// Copyright 2008, Google Inc.
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are met:
+//
+//  1. Redistributions of source code must retain the above copyright notice,
+//     this list of conditions and the following disclaimer.
+//  2. Redistributions in binary form must reproduce the above copyright notice,
+//     this list of conditions and the following disclaimer in the documentation
+//     and/or other materials provided with the distribution.
+//  3. Neither the name of Google Inc. nor the names of its contributors may be
+//     used to endorse or promote products derived from this software without
+//     specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR IMPLIED
+// WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
+// MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO
+// EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
+// PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS;
+// OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
+// WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR
+// OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
+// ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+#ifndef GEARS_GEOLOCATION_EMPTY_DEVICE_DATA_PROVIDER_H__
+#define GEARS_GEOLOCATION_EMPTY_DEVICE_DATA_PROVIDER_H__
+
+#include "gears/geolocation/device_data_provider.h"
+
+// An implementation of DeviceDataProviderImplBase that does not provide any
+// data. Used on platforms where a given data type is not available.
+
+template<typename DataType>
+class EmptyDeviceDataProvider : public DeviceDataProviderImplBase<DataType> {
+ public:
+  EmptyDeviceDataProvider() {}
+  virtual ~EmptyDeviceDataProvider() {}
+
+  // DeviceDataProviderImplBase implementation
+  virtual bool GetData(DataType *data) {
+    assert(data);
+    // This is all the data we can get - nothing.
+    return true;
+  }
+
+ private:
+  DISALLOW_EVIL_CONSTRUCTORS(EmptyDeviceDataProvider);
+};
+
+#endif  // GEARS_GEOLOCATION_EMPTY_DEVICE_DATA_PROVIDER_H__