Add FunctionEntity.asyncMarker and refactor SourceInformationStrategy to avoid ResolvedAst

pkg/compiler/lib/src/ssa/rasta_ssa_builder_task.dart

Index: pkg/compiler/lib/src/ssa/rasta_ssa_builder_task.dart
diff --git a/pkg/compiler/lib/src/ssa/rasta_ssa_builder_task.dart b/pkg/compiler/lib/src/ssa/rasta_ssa_builder_task.dart
index 629a70bf9ad3471c9998151cb77f87bdd9bc76f3..d1cc4ee109ac60cc59ce661d605e749484c8f395 100644
--- a/pkg/compiler/lib/src/ssa/rasta_ssa_builder_task.dart
+++ b/pkg/compiler/lib/src/ssa/rasta_ssa_builder_task.dart
@@ -43,7 +43,7 @@ class RastaSsaBuilderTask extends SsaAstBuilderBase {
           closedWorld,
           work.registry,
           backend.compiler.closureToClassMapper,
-          sourceInformationFactory.createBuilderForContext(resolvedAst),
+          sourceInformationFactory.createBuilderForContext(work.element),
           resolvedAst.kind == ResolvedAstKind.PARSED ? resolvedAst.node : null,
           targetIsConstructorBody: element is ConstructorBodyElement);
       HGraph graph = builder.build();