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

tests/compiler/dart2js/sourcemaps/stacktrace_test.dart

Index: tests/compiler/dart2js/sourcemaps/stacktrace_test.dart
diff --git a/tests/compiler/dart2js/sourcemaps/stacktrace_test.dart b/tests/compiler/dart2js/sourcemaps/stacktrace_test.dart
index 89d1ff7ba671e52a987b9ea9da1a48ec1a63e5b7..90e68fc10f1cdb0ecf3d2a9df47cc447da08001a 100644
--- a/tests/compiler/dart2js/sourcemaps/stacktrace_test.dart
+++ b/tests/compiler/dart2js/sourcemaps/stacktrace_test.dart
@@ -116,6 +116,19 @@ test() {
   '''
 import 'package:expect/expect.dart';
 main() {
+  @{1:main}test(new Class());
+}
+@NoInline()
+test(c) {
+  @{2:test}c.field.method();

[Johnni Winther, 2017/01/25 10:44:20]

Previously the stack trace for this would wrongfully contain mapped frames from
boilerplate code.

[Siggi Cherem (dart-lang), 2017/01/25 16:15:09]

What did the frames look like before?

I'm guessing we want to do something about interceptors for the bug in
https://github.com/dart-lang/sdk/issues/28442, but would this change at least
mean that we no longer have an incorrect mapping to trim()?

[Johnni Winther, 2017/01/26 09:59:14]

It had multiple occurrences of the 'test' frame (for instance from
init.currentScript). The test doesn't scrutinize this. I follow up in other CL -
also verifying the status of 28442.

+}
+class Class {
+  var field;
+}
+''',
+  '''
+import 'package:expect/expect.dart';
+main() {
   // This call is no longer on the stack when the error is thrown.
   @{:main}test();
 }
@@ -308,15 +321,9 @@ Future runTest(int index, Test test,
   }
   List<String> lines = out.split(new RegExp(r'(\r|\n|\r\n)'));
   List<StackTraceLine> jsStackTrace = <StackTraceLine>[];
-  bool seenMarker = false;
   for (String line in lines) {
-    if (seenMarker) {
-      line = line.trim();
-      if (line.startsWith('at ')) {
-        jsStackTrace.add(new StackTraceLine.fromText(line));
-      }
-    } else if (line == EXCEPTION_MARKER) {
-      seenMarker = true;
+    if (line.startsWith('    at ')) {
+      jsStackTrace.add(new StackTraceLine.fromText(line));
     }
   }
 
@@ -324,15 +331,15 @@ Future runTest(int index, Test test,
   for (StackTraceLine line in jsStackTrace) {
     TargetEntry targetEntry = _findColumn(line.lineNo - 1, line.columnNo - 1,
         _findLine(sourceMap, line.lineNo - 1));
-    if (targetEntry == null) {
+    if (targetEntry == null || targetEntry.sourceUrlId == null) {
       dartStackTrace.add(line);
     } else {
       String methodName;
-      if (targetEntry.sourceNameId != 0) {
+      if (targetEntry.sourceNameId != null) {
         methodName = sourceMap.names[targetEntry.sourceNameId];
       }
       String fileName;
-      if (targetEntry.sourceUrlId != 0) {
+      if (targetEntry.sourceUrlId != null) {
         fileName = sourceMap.urls[targetEntry.sourceUrlId];
       }
       dartStackTrace.add(new StackTraceLine(methodName, fileName,