Add some missing virtual destructors to base classes.

base/files/file_tracing.h

 // Copyright 2015 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 BASE_FILES_FILE_TRACING_H_
 #define BASE_FILES_FILE_TRACING_H_
 
 #include "base/base_export.h"
 #include "base/basictypes.h"
 #include "base/macros.h"
 
 #define FILE_TRACING_PREFIX "File"
 
 #define SCOPED_FILE_TRACE_WITH_SIZE(name, size) \
     FileTracing::ScopedTrace scoped_file_trace; \
     if (scoped_file_trace.ShouldInitialize()) \
       scoped_file_trace.Initialize(FILE_TRACING_PREFIX "::" name, this, size)
 
 #define SCOPED_FILE_TRACE(name) SCOPED_FILE_TRACE_WITH_SIZE(name, 0)
 
 namespace base {
 
 class File;
 class FilePath;
 
 class BASE_EXPORT FileTracing {
  public:
   class Provider {
    public:
+    virtual ~Provider() = default;
+
     // Whether the file tracing category is currently enabled.
     virtual bool FileTracingCategoryIsEnabled() const = 0;
 
     // Enables file tracing for |id|. Must be called before recording events.
     virtual void FileTracingEnable(void* id) = 0;
 
     // Disables file tracing for |id|.
     virtual void FileTracingDisable(void* id) = 0;
 
     // Begins an event for |id| with |name|. |path| tells where in the directory
@@ skipping 41 matching lines @@
 
     DISALLOW_COPY_AND_ASSIGN(ScopedTrace);
   };
 
   DISALLOW_COPY_AND_ASSIGN(FileTracing);
 };
 
 }  // namespace base
 
 #endif  // BASE_FILES_FILE_TRACING_H_