Remove all blimp client code.

blimp/client/public/contents/blimp_contents_observer.cc

-// Copyright 2016 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 "blimp/client/public/contents/blimp_contents_observer.h"
-
-#include "blimp/client/public/contents/blimp_contents.h"
-
-namespace blimp {
-namespace client {
-
-BlimpContentsObserver::BlimpContentsObserver(BlimpContents* blimp_contents)
-    : contents_(blimp_contents) {
-  blimp_contents->AddObserver(this);
-}
-
-BlimpContentsObserver::~BlimpContentsObserver() {
-  if (contents_)
-    contents_->RemoveObserver(this);
-}
-
-void BlimpContentsObserver::BlimpContentsDying() {
-  DCHECK(contents_);
-  OnContentsDestroyed();
-  contents_ = nullptr;
-}
-
-}  // namespace client
-}  // namespace blimp