[base] Drop obsolete Thread::YieldCPU.

The method is not used anywhere, and it is a bad idea in general anyway.
If you see a need to call YieldCPU, then you're code is probably in need
of a redesign!

R=svenpanne@chromium.org

Review URL: https://codereview.chromium.org/1116853002

Cr-Commit-Position: refs/heads/master@{#28147}

src/base/platform/platform-posix.cc

@@ -631,13 +631,6 @@ void Thread::Join() {
 }
 
 
-void Thread::YieldCPU() {
-  int result = sched_yield();
-  DCHECK_EQ(0, result);
-  USE(result);
-}
-
-
 static Thread::LocalStorageKey PthreadKeyToLocalKey(pthread_key_t pthread_key) {
 #if V8_OS_CYGWIN
   // We need to cast pthread_key_t to Thread::LocalStorageKey in two steps
@@ -761,5 +754,5 @@ void Thread::SetThreadLocal(LocalStorageKey key, void* value) {
   USE(result);
 }
 
-
-} }  // namespace v8::base
+}  // namespace base
+}  // namespace v8

src/base/platform/platform-win32.cc

@@ -1384,10 +1384,5 @@ void Thread::SetThreadLocal(LocalStorageKey key, void* value) {
   DCHECK(result);
 }
 
-
-
-void Thread::YieldCPU() {
-  Sleep(0);
-}
-
-} }  // namespace v8::base
+}  // namespace base
+}  // namespace v8

src/base/platform/platform.h

@@ -446,10 +446,6 @@ class Thread {
   }
 #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;

test/cctest/test-threads.cc

@@ -70,7 +70,6 @@ class ThreadA : public v8::base::Thread {
     do {
       {
         v8::Unlocker unlocker(CcTest::isolate());
-        Thread::YieldCPU();
       }
     } while (turn != SECOND_TIME_FILL_CACHE);
 
@@ -102,8 +101,6 @@ class ThreadB : public v8::base::Thread {
           break;
         }
       }
-
-      Thread::YieldCPU();
     } while (true);
   }
 };