Replace C++ bitfields with our own BitFields

src/heap-snapshot-generator.cc

Index: src/heap-snapshot-generator.cc
diff --git a/src/heap-snapshot-generator.cc b/src/heap-snapshot-generator.cc
index 68522fccec653dc9c67fda812cfab11ec76b6d7c..7f217bb8d64ecbc2f288b26d6e19bfad40f64211 100644
--- a/src/heap-snapshot-generator.cc
+++ b/src/heap-snapshot-generator.cc
@@ -18,8 +18,7 @@ namespace internal {
 
 
 HeapGraphEdge::HeapGraphEdge(Type type, const char* name, int from, int to)
-    : type_(type),
-      from_index_(from),
+    : bit_field_(TypeField::encode(type) | FromIndexField::encode(from)),
       to_index_(to),
       name_(name) {
   DCHECK(type == kContextVariable
@@ -31,8 +30,7 @@ HeapGraphEdge::HeapGraphEdge(Type type, const char* name, int from, int to)
 
 
 HeapGraphEdge::HeapGraphEdge(Type type, int index, int from, int to)
-    : type_(type),
-      from_index_(from),
+    : bit_field_(TypeField::encode(type) | FromIndexField::encode(from)),
       to_index_(to),
       index_(index) {
   DCHECK(type == kElement || type == kHidden);