Replace C++ bitfields with our own BitFields

src/ast.cc

Index: src/ast.cc
diff --git a/src/ast.cc b/src/ast.cc
index 1df668ddf7ea90ede64991a9a0d175c1c546199e..2dffacaf338b8f12ee51322163c95db89acf8669 100644
--- a/src/ast.cc
+++ b/src/ast.cc
@@ -61,9 +61,9 @@ bool Expression::IsUndefinedLiteral(Isolate* isolate) const {
 
 VariableProxy::VariableProxy(Zone* zone, Variable* var, int position)
     : Expression(zone, position),
-      is_this_(var->is_this()),
-      is_assigned_(false),
-      is_resolved_(false),
+      bit_field_(IsThisField::encode(var->is_this()) |
+                 IsAssignedField::encode(false) |
+                 IsResolvedField::encode(false)),
       variable_feedback_slot_(FeedbackVectorICSlot::Invalid()),
       raw_name_(var->raw_name()),
       interface_(var->interface()) {
@@ -74,9 +74,8 @@ VariableProxy::VariableProxy(Zone* zone, Variable* var, int position)
 VariableProxy::VariableProxy(Zone* zone, const AstRawString* name, bool is_this,
                              Interface* interface, int position)
     : Expression(zone, position),
-      is_this_(is_this),
-      is_assigned_(false),
-      is_resolved_(false),
+      bit_field_(IsThisField::encode(is_this) | IsAssignedField::encode(false) |
+                 IsResolvedField::encode(false)),
       variable_feedback_slot_(FeedbackVectorICSlot::Invalid()),
       raw_name_(name),
       interface_(interface) {}
@@ -99,9 +98,9 @@ void VariableProxy::BindTo(Variable* var) {
 Assignment::Assignment(Zone* zone, Token::Value op, Expression* target,
                        Expression* value, int pos)
     : Expression(zone, pos),
-      is_uninitialized_(false),
-      key_type_(ELEMENT),
-      store_mode_(STANDARD_STORE),
+      bit_field_(IsUninitializedField::encode(false) |
+                 KeyTypeField::encode(ELEMENT) |
+                 StoreModeField::encode(STANDARD_STORE)),
       op_(op),
       target_(target),
       value_(value),