[base] Drop obsolete Thread::YieldCPU.

src/base/platform/platform.h

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // This module contains the platform-specific code. This make the rest of the
 // code less dependent on operating system, compilers and runtime libraries.
 // This module does specifically not deal with differences between different
 // processor architecture.
 // The platform classes have the same definition for all platforms. The
 // implementation for a particular platform is put in platform_<os>.cc.
@@ skipping 428 matching lines @@
         InternalGetExistingThreadLocal(static_cast<intptr_t>(key)));
     DCHECK(result == GetThreadLocal(key));
     return result;
   }
 #else
   static inline void* GetExistingThreadLocal(LocalStorageKey key) {
     return GetThreadLocal(key);
   }
 #endif
 
-  // A hint to the scheduler to let another thread run.
-  static void YieldCPU();
-
-
   // The thread name length is limited to 16 based on Linux's implementation of
   // prctl().
   static const int kMaxThreadNameLength = 16;
 
   class PlatformData;
   PlatformData* data() { return data_; }
 
   void NotifyStartedAndRun() {
     if (start_semaphore_) start_semaphore_->Signal();
     Run();
   }
 
  private:
   void set_name(const char* name);
 
   PlatformData* data_;
 
   char name_[kMaxThreadNameLength];
   int stack_size_;
   Semaphore* start_semaphore_;
 
   DISALLOW_COPY_AND_ASSIGN(Thread);
 };
 
 } }  // namespace v8::base
 
 #endif  // V8_BASE_PLATFORM_PLATFORM_H_