Only generate coverageIds when needed

pkg/compiler/lib/src/dump_info.dart

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library dump_info;
 
 import 'dart:convert'
     show ChunkedConversionSink, JsonEncoder, StringConversionSink;
 
 import 'package:dart2js_info/info.dart';
@@ skipping 112 matching lines @@
     TypeMask inferredType = _resultOf(element).type;
     // If a field has an empty inferred type it is never used.
     if (inferredType == null || inferredType.isEmpty) return null;
 
     int size = compiler.dumpInfoTask.sizeOf(element);
     String code = compiler.dumpInfoTask.codeOf(element);
     if (code != null) size += code.length;
 
     FieldInfo info = new FieldInfo(
         name: element.name,
-        // We use element.hashCode because it is globally unique and it is
-        // available while we are doing codegen.
-        coverageId: '${element.hashCode}',
         type: '${element.type}',
         inferredType: '$inferredType',
         code: code,
         outputUnit: _unitInfoForElement(element),
         isConst: element.isConst);
     _elementToInfo[element] = info;
     if (element.isConst) {
       var value = compiler.backend.constantCompilerTask
           .getConstantValue(element.constant);
       if (value != null) {
         info.initializer = _constantToInfo[value];
       }
     }
 
+    if (JavaScriptBackend.TRACE_METHOD == 'post') {
+      // We use element.hashCode because it is globally unique and it is
+      // available while we are doing codegen.
+      info.coverageId = '${element.hashCode}';
+    }
+
     int closureSize = _addClosureInfo(info, element);
     info.size = size + closureSize;
 
     result.fields.add(info);
     return info;
   }
 
   ClassInfo visitClassElement(ClassElement element, _) {
     ClassInfo classInfo = new ClassInfo(
         name: element.name,
@@ skipping 107 matching lines @@
     }
     String inferredReturnType = '${_resultOf(element).returnType}';
     String sideEffects = '${closedWorld.getSideEffectsOfElement(element)}';
 
     int inlinedCount = compiler.dumpInfoTask.inlineCount[element];
     if (inlinedCount == null) inlinedCount = 0;
 
     FunctionInfo info = new FunctionInfo(
         name: name,
         functionKind: kind,
-        // We use element.hashCode because it is globally unique and it is
-        // available while we are doing codegen.
-        coverageId: '${element.hashCode}',
         modifiers: modifiers,
         returnType: returnType,
         inferredReturnType: inferredReturnType,
         parameters: parameters,
         sideEffects: sideEffects,
         inlinedCount: inlinedCount,
         code: code,
         type: element.type.toString(),
         outputUnit: _unitInfoForElement(element));
     _elementToInfo[element] = info;
 
     if (element is MemberElement) {
       int closureSize = _addClosureInfo(info, element as MemberElement);
       size += closureSize;
     } else {
       info.closures = <ClosureInfo>[];
     }
 
+    if (JavaScriptBackend.TRACE_METHOD == 'post') {
+      // We use element.hashCode because it is globally unique and it is
+      // available while we are doing codegen.
+      info.coverageId = '${element.hashCode}';
+    }
+
     info.size = size;
 
     result.functions.add(info);
     return info;
   }
 
   /// Adds closure information to [info], using all nested closures in [member].
   ///
   /// Returns the total size of the nested closures, to add to the info size.
   int _addClosureInfo(Info info, MemberElement member) {
@@ skipping 292 matching lines @@
 
     ChunkedConversionSink<Object> sink = encoder.startChunkedConversion(
         new StringConversionSink.fromStringSink(buffer));
     sink.add(new AllInfoJsonCodec().encode(result));
     compiler.reporter.reportInfo(NO_LOCATION_SPANNABLE, MessageKind.GENERIC, {
       'text': "View the dumped .info.json file at "
           "https://dart-lang.github.io/dump-info-visualizer"
     });
   }
 }