Simple BlinkGC heap compaction.

third_party/WebKit/Source/wtf/Vector.h

Index: third_party/WebKit/Source/wtf/Vector.h
diff --git a/third_party/WebKit/Source/wtf/Vector.h b/third_party/WebKit/Source/wtf/Vector.h
index 0050854e6daad097fb8ba5cf431a08f2e5a78e3b..a6089891052775ee4424c38cb50e147db68a187d 100644
--- a/third_party/WebKit/Source/wtf/Vector.h
+++ b/third_party/WebKit/Source/wtf/Vector.h
@@ -492,6 +492,8 @@ class VectorBuffer<T, 0, Allocator>
     return buffer();
   }
 
+  T** bufferSlot() { return &m_buffer; }
+
  protected:
   using Base::m_size;
 
@@ -771,6 +773,8 @@ class VectorBuffer : protected VectorBufferBase<T, true, Allocator> {
     return buffer() && buffer() != inlineBuffer();
   }
 
+  T** bufferSlot() { return &m_buffer; }
+
  protected:
   using Base::m_size;
 
@@ -1595,6 +1599,7 @@ void Vector<T, inlineCapacity, Allocator>::trace(VisitorDispatcher visitor) {
     if (Allocator::isHeapObjectAlive(buffer()))
       return;
     Allocator::markNoTracing(visitor, buffer());
+    Allocator::registerBackingStoreReference(visitor, Base::bufferSlot());
   }
   const T* bufferBegin = buffer();
   const T* bufferEnd = buffer() + size();