dart2js: add function coverage tracking in dart2js output, dumpinfo, and

pkg/compiler/lib/src/js_backend/backend.dart

Index: pkg/compiler/lib/src/js_backend/backend.dart
diff --git a/pkg/compiler/lib/src/js_backend/backend.dart b/pkg/compiler/lib/src/js_backend/backend.dart
index bdd1cc3a191627127c1f758e0476e1f6ecff0083..a6aff4b0a211d913c0acaf45959430b43f7e2e66 100644
--- a/pkg/compiler/lib/src/js_backend/backend.dart
+++ b/pkg/compiler/lib/src/js_backend/backend.dart
@@ -1451,7 +1451,15 @@ class JavaScriptBackend extends Backend {
       }
     }
 
-    generatedCode[element] = functionCompiler.compile(work);
+    jsAst.Fun code = functionCompiler.compile(work);
+    if (const bool.fromEnvironment('instrumentForCoverage')
+        && compiler.dumpInfo) {
+      // TODO(sigmund): do this properly (e.g. add an embedded global, etc).
+      code.body.statements.insert(0, js.statement(
+          '__record_use("${element.hashCode}", "${element.name}")'));
+    }
+
+    generatedCode[element] = code;
     return const WorldImpact();
   }