Fix "unused variable" warnings.

content/browser/media/capture/window_activity_tracker_mac.mm

 // 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 "content/browser/media/capture/window_activity_tracker_mac.h"
 
 #include <AppKit/AppKit.h>
 #include <CoreFoundation/CoreFoundation.h>
 
 #include "base/bind.h"
@@ skipping 42 matching lines @@
 namespace content {
 
 // static
 std::unique_ptr<WindowActivityTracker> WindowActivityTracker::Create(
     gfx::NativeView view) {
   return std::unique_ptr<WindowActivityTracker>(
       new WindowActivityTrackerMac(view));
 }
 
 WindowActivityTrackerMac::WindowActivityTrackerMac(NSView* view)
-    : view_(view), weak_factory_(this) {
+    : weak_factory_(this) {
   mouse_tracker_.reset([[MouseTracker alloc] initWithView:view]);
   [mouse_tracker_ registerMouseInteractionObserver:
                       base::Bind(&WindowActivityTrackerMac::OnMouseActivity,
                                  base::Unretained(this))];
 }
 
 WindowActivityTrackerMac::~WindowActivityTrackerMac() {
   [mouse_tracker_ stopTracking];
 }
 
 void WindowActivityTrackerMac::OnMouseActivity() {
   WindowActivityTracker::OnMouseActivity();
 }
 
 base::WeakPtr<WindowActivityTracker> WindowActivityTrackerMac::GetWeakPtr() {
   return weak_factory_.GetWeakPtr();
 }
 
 }  // namespace content