Merge the Merlin heap tracing to top-of-trunk.

runtime/vm/raw_object.h

Index: runtime/vm/raw_object.h
diff --git a/runtime/vm/raw_object.h b/runtime/vm/raw_object.h
index ca98af4a6dd515c03dbfcb72b481743268af2430..8f0fc9c82cec4afc2811313123772cd39f4a87f2 100644
--- a/runtime/vm/raw_object.h
+++ b/runtime/vm/raw_object.h
@@ -387,6 +387,10 @@ class RawObject {
   friend class Heap;
   friend class HeapProfiler;
   friend class HeapProfilerRootVisitor;
+  friend class HeapTrace;
+  friend class HeapTraceDebugObjectVisitor;
+  friend class HeapTraceHandleVisitor;
+  friend class HeapTraceVisitor;
   friend class MarkingVisitor;
   friend class Object;
   friend class RawInstructions;
@@ -440,6 +444,7 @@ class RawClass : public RawObject {
   intptr_t token_pos_;
   uint8_t state_bits_;  // state, is_const, is_interface, is_implemented.
 
+  friend class HeapTrace;
   friend class Instance;
   friend class Object;
   friend class RawInstance;
@@ -1116,6 +1121,8 @@ class RawString : public RawInstance {
   RawSmi* length_;
   RawSmi* hash_;
   RawObject** to() { return reinterpret_cast<RawObject**>(&ptr()->hash_); }
+
+  friend class HeapTrace;
 };
 
 
@@ -1125,8 +1132,9 @@ class RawOneByteString : public RawString {
   // Variable length data follows here.
   uint8_t data_[0];
 
-  friend class SnapshotReader;
   friend class ApiMessageReader;
+  friend class HeapTrace;
+  friend class SnapshotReader;
 };
 
 
@@ -1136,6 +1144,7 @@ class RawTwoByteString : public RawString {
   // Variable length data follows here.
   uint16_t data_[0];
 
+  friend class HeapTrace;
   friend class SnapshotReader;
 };
 
@@ -1215,6 +1224,7 @@ class RawArray : public RawInstance {
 class RawImmutableArray : public RawArray {
   RAW_HEAP_OBJECT_IMPLEMENTATION(ImmutableArray);
 
+  friend class HeapTrace;
   friend class SnapshotReader;
 };