[base] Drop obsolete Thread::YieldCPU.

test/cctest/test-threads.cc

 // Copyright 2008 the V8 project authors. 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
@@ skipping 52 matching lines @@
           "  var result = \"a\".search(\"a\");"
           "  if (result != 0) throw \"result: \" + result + \" @\" + i;"
           "};"
           "true"));
     CHECK(script->Run()->IsTrue());
 
     turn = CLEAN_CACHE;
     do {
       {
         v8::Unlocker unlocker(CcTest::isolate());
-        Thread::YieldCPU();
       }
     } while (turn != SECOND_TIME_FILL_CACHE);
 
     // Rerun the script.
     CHECK(script->Run()->IsTrue());
 
     turn = DONE;
   }
 };
 
@@ skipping 11 matching lines @@
           v8::HandleScope scope(isolate);
           v8::Handle<v8::Context> context = v8::Context::New(isolate);
           v8::Context::Scope context_scope(context);
 
           // Clear the caches by forcing major GC.
           CcTest::heap()->CollectAllGarbage();
           turn = SECOND_TIME_FILL_CACHE;
           break;
         }
       }
-
-      Thread::YieldCPU();
     } while (true);
   }
 };
 
 
 TEST(JSFunctionResultCachesInTwoThreads) {
   ThreadA threadA;
   ThreadB threadB;
 
   threadA.Start();
@@ skipping 51 matching lines @@
     refs.Add(i::ThreadId::Invalid());
   }
   prev->Start();
   for (int i = 0; i < kNThreads; i++) {
     semaphore.Wait();
   }
   for (int i = 0; i < kNThreads; i++) {
     delete threads[i];
   }
 }