Include thread CPU time in Timeline

runtime/vm/os.h

Index: runtime/vm/os.h
diff --git a/runtime/vm/os.h b/runtime/vm/os.h
index cd570c4bcabe650095a21cc7455d064f5dc8f6d5..906432240bbf79dc7d38945796ff55f9e615c2be 100644
--- a/runtime/vm/os.h
+++ b/runtime/vm/os.h
@@ -56,6 +56,13 @@ class OS {
   // Returns the frequency of the monotonic clock.
   static int64_t GetCurrentMonotonicFrequency();
 
+  // Returns the value of current thread's CPU usage clock in microseconds.
+  // NOTE: This clock will return different values depending on the calling
+  // thread. It is only expected to increase in value as the thread uses
+  // CPU time.
+  // NOTE: This function will return -1 on OSs that are not supported.
+  static int64_t GetCurrentThreadCPUMicros();
+
   // Returns a cleared aligned array of type T with n entries.
   // Alignment must be >= 16 and a power of two.
   template<typename T>