Add no-info mappings at start of out.js and after mapped functions

pkg/compiler/lib/src/io/position_information.dart

Index: pkg/compiler/lib/src/io/position_information.dart
diff --git a/pkg/compiler/lib/src/io/position_information.dart b/pkg/compiler/lib/src/io/position_information.dart
index a3169300993e9c8237ebb0892032c24c8155196e..17e83978dd51fbd065e305e29977e4b029724188 100644
--- a/pkg/compiler/lib/src/io/position_information.dart
+++ b/pkg/compiler/lib/src/io/position_information.dart
@@ -520,11 +520,17 @@ class PositionTraceListener extends TraceListener
 
   @override
   void onStep(js.Node node, Offset offset, StepKind kind) {
-    SourceInformation sourceInformation = computeSourceInformation(node);
-    if (sourceInformation == null) return;
     int codeLocation = offset.value;
     if (codeLocation == null) return;
 
+    if (kind == StepKind.NO_INFO) {
+      sourceMapper.register(node, codeLocation, const NoSourceLocationMarker());
+      return;
+    }
+
+    SourceInformation sourceInformation = computeSourceInformation(node);
+    if (sourceInformation == null) return;
+
     void registerPosition(SourcePositionKind sourcePositionKind) {
       SourceLocation sourceLocation =
           getSourceLocation(sourceInformation, sourcePositionKind);
@@ -562,6 +568,8 @@ class PositionTraceListener extends TraceListener
       case StepKind.SWITCH_EXPRESSION:
         registerPosition(SourcePositionKind.START);
         break;
+      case StepKind.NO_INFO:
+        break;
     }
   }
 }
@@ -710,6 +718,7 @@ enum StepKind {
   WHILE_CONDITION,
   DO_CONDITION,
   SWITCH_EXPRESSION,
+  NO_INFO,
 }
 
 /// Listener for the [JavaScriptTracer].
@@ -775,14 +784,20 @@ class JavaScriptTracer extends js.BaseVisitor {
     }
   }
 
-  void notifyStep(js.Node node, Offset offset, StepKind kind) {
-    if (active) {
+  void notifyStep(js.Node node, Offset offset, StepKind kind,
+      {bool force: false}) {
+    if (active || force) {
       listeners.forEach((listener) => listener.onStep(node, offset, kind));
     }
   }
 
   void apply(js.Node node) {
     notifyStart(node);
+
+    int startPosition = getSyntaxOffset(node, kind: CodePositionKind.START);
+    Offset startOffset = getOffsetForNode(node, startPosition);
+    notifyStep(node, startOffset, StepKind.NO_INFO, force: true);
+
     node.accept(this);
     notifyEnd(node);
   }
@@ -829,6 +844,11 @@ class JavaScriptTracer extends js.BaseVisitor {
         statementOffset = getSyntaxOffset(node, kind: CodePositionKind.CLOSING);
     Offset exitOffset = getOffsetForNode(node, statementOffset);
     notifyStep(node, exitOffset, StepKind.FUN_EXIT);
+    if (active && !activeBefore) {
+      int endPosition = getSyntaxOffset(node, kind: CodePositionKind.END);
+      Offset endOffset = getOffsetForNode(node, endPosition);
+      notifyStep(node, endOffset, StepKind.NO_INFO);
+    }
     active = activeBefore;
   }