Oilpan: Add trace events for the GC marking and sweeping phases.

Source/platform/heap/ThreadState.h

 /*
  * Copyright (C) 2013 Google Inc. 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
@@ skipping 261 matching lines @@
 public:
     // When garbage collecting we need to know whether or not there
     // can be pointers to Blink GC managed objects on the stack for
     // each thread. When threads reach a safe point they record
     // whether or not they have pointers on the stack.
     enum StackState {
         NoHeapPointersOnStack,
         HeapPointersOnStack
     };
 
+    // When profiling we would like to identify forced GC requests.
+    enum CauseOfGC {
+        NormalGC,
+        ForcedGC
+    };
+
     class NoSweepScope {
     public:
         explicit NoSweepScope(ThreadState* state) : m_state(state)
         {
             ASSERT(!m_state->m_sweepInProgress);
             m_state->m_sweepInProgress = true;
         }
         ~NoSweepScope()
         {
             ASSERT(m_state->m_sweepInProgress);
@@ skipping 549 matching lines @@
     // whether the page is part of a terminting thread or
     // if the page is traced after being terminated (orphaned).
     uintptr_t m_terminating : 1;
     uintptr_t m_tracedAfterOrphaned : 1;
     uintptr_t m_promptlyFreedSize : 17; // == blinkPageSizeLog2
 };
 
 }
 
 #endif // ThreadState_h