Add OS::GetCurrentProcessId and prepend output from trace-gc with the current pid

src/incremental-marking-inl.h

 // Copyright 2012 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 89 matching lines @@
   int64_t old_bytes_rescanned = bytes_rescanned_;
   bytes_rescanned_ = old_bytes_rescanned + obj_size;
   if ((bytes_rescanned_ >> 20) != (old_bytes_rescanned >> 20)) {
     if (bytes_rescanned_ > 2 * heap_->PromotedSpaceSizeOfObjects()) {
       // If we have queued twice the heap size for rescanning then we are
       // going around in circles, scanning the same objects again and again
       // as the program mutates the heap faster than we can incrementally
       // trace it.  In this case we switch to non-incremental marking in
       // order to finish off this marking phase.
       if (FLAG_trace_gc) {
-        PrintF("Hurrying incremental marking because of lack of progress\n");
+        PrintPID("Hurrying incremental marking because of lack of progress\n");
       }
       allocation_marking_factor_ = kMaxAllocationMarkingFactor;
     }
   }
 
   marking_deque_.UnshiftGrey(obj);
 }
 
 
 void IncrementalMarking::WhiteToGreyAndPush(HeapObject* obj, MarkBit mark_bit) {
@@ skipping 19 matching lines @@
     MemoryChunk::IncrementLiveBytesFromGC(obj->address(), obj->Size());
     return true;
   }
   return false;
 }
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_INCREMENTAL_MARKING_INL_H_