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diff --git a/net/base/dns_resolution_observer.cc b/net/base/dns_resolution_observer.cc
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+++ b/net/base/dns_resolution_observer.cc
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+// Copyright 2008, Google Inc.
+// All rights reserved.
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//    * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//    * 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.
+//    * 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 COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "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 COPYRIGHT
+// OWNER OR CONTRIBUTORS 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.
+
+// This file supports network stack independent notification of progress
+// towards resolving a hostname.
+
+#include "net/base/dns_resolution_observer.h"
+
+#include <string>
+
+#include "base/atomic.h"
+#include "base/logging.h"
+
+namespace net {
+
+static DnsResolutionObserver* dns_resolution_observer;
+
+void AddDnsResolutionObserver(DnsResolutionObserver* new_observer) {
+  if (new_observer == dns_resolution_observer)
+    return;  // Facilitate unit tests that init/teardown repeatedly.
+  DCHECK(!dns_resolution_observer);
+  if (InterlockedCompareExchangePointer(
+          reinterpret_cast<PVOID*>(&dns_resolution_observer),
+          new_observer, NULL))
+    DCHECK(0) << "Second attempt to setup observer";
+}
+
+DnsResolutionObserver* RemoveDnsResolutionObserver() {
+  // We really need to check that the entire network subsystem is shutting down,
+  // and hence no additional calls can even *possibly* still be lingering in the
+  // notification path that includes our observer.  Until we have a way to
+  // really assert that fact, we will outlaw the calling of this function.
+  // Darin suggested that the caller use a static initializer for the observer,
+  // so that it can safely be destroyed after process termination, and without
+  // inducing a memory leak.
+  // Bottom line: Don't call this function!  You will crash for now.
+  CHECK(0);
+  DnsResolutionObserver* old_observer = dns_resolution_observer;
+  dns_resolution_observer = NULL;
+  return old_observer;
+}
+
+// Locking access to dns_resolution_observer is not really critical... but we
+// should test the value of dns_resolution_observer that we use.
+// Worst case, we'll get an "out of date" value... which is no big deal for the
+// DNS prefetching system (the most common (only?) observer).
+void DidStartDnsResolution(const std::string& name, void* context) {
+  DnsResolutionObserver* current_observer = dns_resolution_observer;
+  if (current_observer)
+    current_observer->OnStartResolution(name, context);
+}
+
+void DidFinishDnsResolutionWithStatus(bool was_resolved, void* context) {
+  DnsResolutionObserver* current_observer = dns_resolution_observer;
+  if (current_observer) {
+    current_observer->OnFinishResolutionWithStatus(was_resolved, context);
+  }
+}
+}  // namspace net