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 bf5164e5fc640b7e9e31cf4d9522e13bef9cc61a..dfa7a5974157979c2ba07f3d99addfbdd9219626 100644
--- a/runtime/vm/raw_object.h
+++ b/runtime/vm/raw_object.h
@@ -390,6 +390,10 @@ 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;
@@ -443,6 +447,7 @@ class RawClass : public RawObject {
   intptr_t token_pos_;
   uint8_t state_bits_;  // state, is_const, is_implemented.
 
+  friend class HeapTrace;
   friend class Instance;
   friend class Object;
   friend class RawInstance;
@@ -1135,6 +1140,8 @@ class RawString : public RawInstance {
   RawSmi* length_;
   RawSmi* hash_;
   RawObject** to() { return reinterpret_cast<RawObject**>(&ptr()->hash_); }
+
+  friend class HeapTrace;
 };
 
 
@@ -1144,8 +1151,9 @@ 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;
 };
 
 
@@ -1155,6 +1163,7 @@ class RawTwoByteString : public RawString {
   // Variable length data follows here.
   uint16_t data_[0];
 
+  friend class HeapTrace;
   friend class SnapshotReader;
 };
 
@@ -1234,6 +1243,7 @@ class RawArray : public RawInstance {
 class RawImmutableArray : public RawArray {
   RAW_HEAP_OBJECT_IMPLEMENTATION(ImmutableArray);
 
+  friend class HeapTrace;
   friend class SnapshotReader;
 };