Fix "unused variable" warnings.

cc/trees/single_thread_proxy.h

 // Copyright 2011 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.
 
 #ifndef CC_TREES_SINGLE_THREAD_PROXY_H_
 #define CC_TREES_SINGLE_THREAD_PROXY_H_
 
 #include <limits>
 
 #include "base/cancelable_callback.h"
@@ skipping 157 matching lines @@
 
   base::WeakPtrFactory<SingleThreadProxy> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(SingleThreadProxy);
 };
 
 // For use in the single-threaded case. In debug builds, it pretends that the
 // code is running on the impl thread to satisfy assertion checks.
 class DebugScopedSetImplThread {
  public:
+#if DCHECK_IS_ON()
   explicit DebugScopedSetImplThread(TaskRunnerProvider* task_runner_provider)
       : task_runner_provider_(task_runner_provider) {
-#if DCHECK_IS_ON()
     previous_value_ = task_runner_provider_->impl_thread_is_overridden_;
     task_runner_provider_->SetCurrentThreadIsImplThread(true);
+  }
+#else
+  explicit DebugScopedSetImplThread(TaskRunnerProvider* task_runner_provider) {}
 #endif
-  }
+
   ~DebugScopedSetImplThread() {
 #if DCHECK_IS_ON()
     task_runner_provider_->SetCurrentThreadIsImplThread(previous_value_);
 #endif
   }
 
  private:
+#if DCHECK_IS_ON()
   bool previous_value_;
   TaskRunnerProvider* task_runner_provider_;
+#endif
 
   DISALLOW_COPY_AND_ASSIGN(DebugScopedSetImplThread);
 };
 
 // For use in the single-threaded case. In debug builds, it pretends that the
 // code is running on the main thread to satisfy assertion checks.
 class DebugScopedSetMainThread {
  public:
+#if DCHECK_IS_ON()
   explicit DebugScopedSetMainThread(TaskRunnerProvider* task_runner_provider)
       : task_runner_provider_(task_runner_provider) {
-#if DCHECK_IS_ON()
     previous_value_ = task_runner_provider_->impl_thread_is_overridden_;
     task_runner_provider_->SetCurrentThreadIsImplThread(false);
+  }
+#else
+  explicit DebugScopedSetMainThread(TaskRunnerProvider* task_runner_provider) {}
 #endif
-  }
+
   ~DebugScopedSetMainThread() {
 #if DCHECK_IS_ON()
     task_runner_provider_->SetCurrentThreadIsImplThread(previous_value_);
 #endif
   }
 
  private:
+#if DCHECK_IS_ON()
   bool previous_value_;
   TaskRunnerProvider* task_runner_provider_;
+#endif
 
   DISALLOW_COPY_AND_ASSIGN(DebugScopedSetMainThread);
 };
 
 // For use in the single-threaded case. In debug builds, it pretends that the
 // code is running on the impl thread and that the main thread is blocked to
 // satisfy assertion checks
 class DebugScopedSetImplThreadAndMainThreadBlocked {
  public:
   explicit DebugScopedSetImplThreadAndMainThreadBlocked(
       TaskRunnerProvider* task_runner_provider)
       : impl_thread_(task_runner_provider),
         main_thread_blocked_(task_runner_provider) {}
 
  private:
   DebugScopedSetImplThread impl_thread_;
   DebugScopedSetMainThreadBlocked main_thread_blocked_;
 
   DISALLOW_COPY_AND_ASSIGN(DebugScopedSetImplThreadAndMainThreadBlocked);
 };
 
 }  // namespace cc
 
 #endif  // CC_TREES_SINGLE_THREAD_PROXY_H_