[Kernel] replace function debuggable field with originalAsyncMarker field

pkg/kernel/lib/ast.dart

Index: pkg/kernel/lib/ast.dart
diff --git a/pkg/kernel/lib/ast.dart b/pkg/kernel/lib/ast.dart
index 2f3cb111d74337e809f435bacbdfa2000ae8f9db..60544c9894800be38e684f0de0d6e792f94e7a5d 100644
--- a/pkg/kernel/lib/ast.dart
+++ b/pkg/kernel/lib/ast.dart
@@ -1151,7 +1151,7 @@ class FunctionNode extends TreeNode {
   int fileEndOffset = TreeNode.noOffset;
 
   AsyncMarker asyncMarker;
-  bool debuggable = true;
+  AsyncMarker originalAsyncMarker;

[asgerf, 2017/02/17 13:31:30]

Could you please add some documentation, explaining why there are two async
markers?

[jensj, 2017/02/20 09:06:28]

Done.

   List<TypeParameter> typeParameters;
   int requiredParameterCount;
   List<VariableDeclaration> positionalParameters;
@@ -1167,7 +1167,8 @@ class FunctionNode extends TreeNode {
       int requiredParameterCount,
       this.returnType: const DynamicType(),
       this.inferredReturnValue,
-      this.asyncMarker: AsyncMarker.Sync})
+      this.asyncMarker: AsyncMarker.Sync,
+      this.originalAsyncMarker: AsyncMarker.Sync})
       : this.positionalParameters =
             positionalParameters ?? <VariableDeclaration>[],
         this.requiredParameterCount =