net: Fix more clang warnings about missing virtual and OVERRIDE annotations.

net/disk_cache/file_posix.cc

Index: net/disk_cache/file_posix.cc
diff --git a/net/disk_cache/file_posix.cc b/net/disk_cache/file_posix.cc
index e03d9557965e1a26e8ab84dfbbd127eebe69bb61..c334f28362b3d1c4692be5e2dfcb0383fcb4f7bd 100644
--- a/net/disk_cache/file_posix.cc
+++ b/net/disk_cache/file_posix.cc
@@ -49,7 +49,7 @@ class FileBackgroundIO : public disk_cache::BackgroundIO {
   void Write();
 
  private:
-  ~FileBackgroundIO() {}
+  virtual ~FileBackgroundIO() {}
 
   disk_cache::FileIOCallback* callback_;
 
@@ -66,7 +66,7 @@ class FileBackgroundIO : public disk_cache::BackgroundIO {
 class FileInFlightIO : public disk_cache::InFlightIO {
  public:
   FileInFlightIO() {}
-  ~FileInFlightIO() {}
+  virtual ~FileInFlightIO() {}
 
   // These methods start an asynchronous operation. The arguments have the same
   // semantics of the File asynchronous operations, with the exception that the
@@ -82,7 +82,7 @@ class FileInFlightIO : public disk_cache::InFlightIO {
   // queued (because we are inside WaitForPendingIO), and false if said task is
   // the one performing the call.
   virtual void OnOperationComplete(disk_cache::BackgroundIO* operation,
-                                   bool cancel);
+                                   bool cancel) OVERRIDE;
 
  private:
   DISALLOW_COPY_AND_ASSIGN(FileInFlightIO);