[kernel] Add flag on Procedures for forwarding semi stubs.

Change-Id: I6e39557e9ed2e636a8f43e8835ae797e3fd8b0c2
Reviewed-on: https://dart-review.googlesource.com/29721
Reviewed-by: Paul Berry <paulberry@google.com>
Reviewed-by: Kevin Millikin <kmillikin@google.com>
Commit-Queue: Samir Jindel <sjindel@google.com>

pkg/kernel/binary.md

@@ -349,7 +349,7 @@ type Procedure extends Member {
   FileOffset fileEndOffset;
   Byte kind; // Index into the ProcedureKind enum above.
   Byte flags (isStatic, isAbstract, isExternal, isConst, isForwardingStub,
-              isGenericContravariant);
+              isGenericContravariant, isForwardingSemiStub);
   Name name;
   // An absolute path URI to the .dart file from which the class was created.
   UriReference fileUri;

pkg/kernel/lib/ast.dart

@@ -1496,6 +1496,7 @@ class Procedure extends Member implements FileUriNode {
       bool isExternal: false,
       bool isConst: false,
       bool isForwardingStub: false,
+      bool isForwardingSemiStub: false,
       int transformerFlags: 0,
       this.fileUri,
       Reference reference})
@@ -1515,6 +1516,7 @@ class Procedure extends Member implements FileUriNode {
   static const int FlagConst = 1 << 3; // Only for external const factories.
   static const int FlagForwardingStub = 1 << 4;
   static const int FlagGenericContravariant = 1 << 5;
+  static const int FlagForwardingSemiStub = 1 << 6;
 
   bool get isStatic => flags & FlagStatic != 0;
   bool get isAbstract => flags & FlagAbstract != 0;
@@ -1534,6 +1536,10 @@ class Procedure extends Member implements FileUriNode {
   /// front end computational overhead.
   bool get isGenericContravariant => flags & FlagGenericContravariant != 0;
 
+  /// If set, this flag indicates that although this function is a forwarding
+  /// stub, it was present in the original source as an abstract method.
+  bool get isForwardingSemiStub => flags & FlagForwardingSemiStub != 0;
+
   void set isStatic(bool value) {
     flags = value ? (flags | FlagStatic) : (flags & ~FlagStatic);
   }
@@ -1561,6 +1567,12 @@ class Procedure extends Member implements FileUriNode {
         : (flags & ~FlagGenericContravariant);
   }
 
+  void set isForwardingSemiStub(bool value) {
+    flags = value
+        ? (flags | FlagForwardingSemiStub)
+        : (flags & ~FlagForwardingSemiStub);
+  }
+
   bool get isInstanceMember => !isStatic;
   bool get isGetter => kind == ProcedureKind.Getter;
   bool get isSetter => kind == ProcedureKind.Setter;

pkg/kernel/lib/clone.dart

@@ -401,9 +401,11 @@ class CloneVisitor extends TreeVisitor {
         isExternal: node.isExternal,
         isConst: node.isConst,
         isForwardingStub: node.isForwardingStub,
+        isForwardingSemiStub: node.isForwardingSemiStub,
         transformerFlags: node.transformerFlags,
         fileUri: node.fileUri)
-      ..fileEndOffset = node.fileEndOffset;
+      ..fileEndOffset = node.fileEndOffset
+      ..isGenericContravariant = node.isGenericContravariant;
   }
 
   visitField(Field node) {

pkg/kernel/lib/text/ast_to_text.dart

@@ -904,6 +904,7 @@ class Printer extends Visitor<Null> {
     writeModifier(node.isStatic, 'static');
     writeModifier(node.isAbstract, 'abstract');
     writeModifier(node.isForwardingStub, 'forwarding-stub');
+    writeModifier(node.isForwardingSemiStub, 'forwarding-semi-stub');
     writeModifier(node.isGenericContravariant, 'generic-contravariant');
     writeWord(procedureKindToString(node.kind));
     if ((node.enclosingClass == null &&