Fix error checking in VisitedLinkMaster.

chrome/browser/visitedlink/visitedlink_master.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 "chrome/browser/visitedlink/visitedlink_master.h"
 
 #if defined(OS_WIN)
 #include <windows.h>
 #include <io.h>
 #include <shlobj.h>
@@ skipping 76 matching lines @@
   int ret = fflush(file);
   DCHECK_EQ(0, ret);
   return num_written == data_len;
 }
 
 // This task executes on a background thread and executes a write. This
 // prevents us from blocking the UI thread doing I/O. Double pointer to FILE
 // is used because file may still not be opened by the time of scheduling
 // the task for execution.
 void AsyncWrite(FILE** file, int32 offset, const std::string& data) {
-  WriteToFile(*file, offset, data.data(), data.size());
+  if (*file)
+    WriteToFile(*file, offset, data.data(), data.size());
 }
 
 // Truncates the file to the current position asynchronously on a background
 // thread. Double pointer to FILE is used because file may still not be opened
 // by the time of scheduling the task for execution.
 void AsyncTruncate(FILE** file) {
-  base::IgnoreResult(TruncateFile(*file));
+  if (*file)
+    base::IgnoreResult(TruncateFile(*file));
 }
 
 // Closes the file on a background thread and releases memory used for storage
 // of FILE* value. Double pointer to FILE is used because file may still not
 // be opened by the time of scheduling the task for execution.
 void AsyncClose(FILE** file) {
-  base::IgnoreResult(fclose(*file));
+  if (*file)
+    base::IgnoreResult(fclose(*file));
   free(file);
 }
 
 }  // namespace
 
 // TableBuilder ---------------------------------------------------------------
 
 // How rebuilding from history works
 // ---------------------------------
 //
@@ skipping 851 matching lines @@
 }
 
 void VisitedLinkMaster::TableBuilder::OnCompleteMainThread() {
   if (master_)
     master_->OnTableRebuildComplete(success_, fingerprints_);
 
   // WILL (generally) DELETE THIS! This balances the AddRef in
   // VisitedLinkMaster::RebuildTableFromHistory.
   Release();
 }