Add runtime/bin/thread_fuchsia that binds to fuchsia's pthreads

runtime/bin/thread_fuchsia.cc

Index: runtime/bin/thread_fuchsia.cc
diff --git a/runtime/bin/thread_linux.cc b/runtime/bin/thread_fuchsia.cc
similarity index 95%
copy from runtime/bin/thread_linux.cc
copy to runtime/bin/thread_fuchsia.cc
index 6ea923ea13675fbb2d3e940c30af0af255a51c92..dda960946a07118e21b9857821382c8d454a9a40 100644
--- a/runtime/bin/thread_linux.cc
+++ b/runtime/bin/thread_fuchsia.cc
@@ -3,10 +3,10 @@
 // BSD-style license that can be found in the LICENSE file.
 
 #include "platform/globals.h"
-#if defined(TARGET_OS_LINUX)
+#if defined(TARGET_OS_FUCHSIA)
 
 #include "bin/thread.h"
-#include "bin/thread_linux.h"
+#include "bin/thread_fuchsia.h"
 
 #include <errno.h>  // NOLINT
 #include <sys/resource.h>  // NOLINT
@@ -168,13 +168,7 @@ bool Thread::Compare(ThreadId a, ThreadId b) {
 
 
 void Thread::GetThreadCpuUsage(ThreadId thread_id, int64_t* cpu_usage) {
-  ASSERT(thread_id == GetCurrentThreadId());
-  ASSERT(cpu_usage != NULL);
-  struct timespec ts;
-  int r = clock_gettime(CLOCK_THREAD_CPUTIME_ID, &ts);
-  ASSERT(r == 0);
-  *cpu_usage = (ts.tv_sec * kNanosecondsPerSecond + ts.tv_nsec) /
-               kNanosecondsPerMicrosecond;
+  UNIMPLEMENTED();
 }
 
 
@@ -334,4 +328,4 @@ void Monitor::NotifyAll() {
 }  // namespace bin
 }  // namespace dart
 
-#endif  // defined(TARGET_OS_LINUX)
+#endif  // defined(TARGET_OS_FUCHSIA)