[tracing] Adding class-wise memory statistics to blink gc memory dumps

Source/platform/heap/ThreadState.h

Index: Source/platform/heap/ThreadState.h
diff --git a/Source/platform/heap/ThreadState.h b/Source/platform/heap/ThreadState.h
index 0c015aeee37db03a46d4f7c03e250cddb3e39ba8..90943d4d616e777b74f80a24620385a4baded7d8 100644
--- a/Source/platform/heap/ThreadState.h
+++ b/Source/platform/heap/ThreadState.h
@@ -499,6 +499,16 @@ public:
     // Visit all persistents allocated on this thread.
     void visitPersistents(Visitor*);
 
+    struct GCSnapshotInfo {
+        GCSnapshotInfo(size_t numObjectTypes);
+
+        // Map from gcInfoIndex (vector-index) to count/size.
+        Vector<int> liveCount;
+        Vector<int> deadCount;
+        Vector<size_t> liveSize;
+        Vector<size_t> deadSize;
+    };
+
 #if ENABLE(GC_PROFILING)
     const GCInfo* findGCInfo(Address);
     static const GCInfo* findGCInfoFromAllThreads(Address);