Removed unnecessary string concatenations

runtime/observatory/lib/src/elements/cpu_profile/virtual_tree.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.
 
 import 'dart:async';
 import 'dart:html';
 import 'dart:math' as Math;
 import 'package:observatory/models.dart' as M;
 import 'package:observatory/src/elements/stack_trace_tree_config.dart'
     show ProfileTreeMode;
@@ skipping 187 matching lines @@
     element.children[5] = new FunctionRefElement(
         _isolate, item.profileFunction.function,
         queue: _r.queue)
       ..classes = ['name'];
   }
 
   void _updateMemoryFunctionRow(
       HtmlElement element, M.FunctionCallTreeNode item, int depth) {
     element.children[0].text =
         Utils.formatSize(item.inclusiveNativeAllocations);
-    element.children[0].title = 'memory allocated from resulting calls: ' +
+    element.children[0].title = 'memory allocated from resulting calls: '
         '${item.inclusiveNativeAllocations}B';
     element.children[1].text =
         Utils.formatSize(item.exclusiveNativeAllocations);
-    element.children[1].title = 'memory allocated during execution: ' +
+    element.children[1].title = 'memory allocated during execution: '
         '${item.exclusiveNativeAllocations}B';
     _updateLines(element.children[2].children, depth);
     if (item.children.isNotEmpty) {
       element.children[3].text =
           _tree.isExpanded(item) ? _expandedIcon : _collapsedIcon;
     } else {
       element.children[3].text = '';
     }
     element.children[4].text = Utils.formatPercentNormalized(item.percentage);
     element.children[5] = new FunctionRefElement(
@@ skipping 18 matching lines @@
     element.children[4].text = Utils.formatPercentNormalized(item.percentage);
     element.children[5] =
         new CodeRefElement(_isolate, item.profileCode.code, queue: _r.queue)
           ..classes = ['name'];
   }
 
   void _updateMemoryCodeRow(
       HtmlElement element, M.CodeCallTreeNode item, int depth) {
     element.children[0].text =
         Utils.formatSize(item.inclusiveNativeAllocations);
-    element.children[0].title = 'memory allocated from resulting calls: ' +
+    element.children[0].title = 'memory allocated from resulting calls: '
         '${item.inclusiveNativeAllocations}B';
     element.children[1].text =
         Utils.formatSize(item.exclusiveNativeAllocations);
-    element.children[1].title = 'memory allocated during execution: ' +
+    element.children[1].title = 'memory allocated during execution: '
         '${item.exclusiveNativeAllocations}B';
     _updateLines(element.children[2].children, depth);
     if (item.children.isNotEmpty) {
       element.children[3].text =
           _tree.isExpanded(item) ? _expandedIcon : _collapsedIcon;
     } else {
       element.children[3].text = '';
     }
     element.children[4].text = Utils.formatPercentNormalized(item.percentage);
     element.children[5] =
         new CodeRefElement(null, item.profileCode.code, queue: _r.queue)
           ..classes = ['name'];
   }
 
   static _updateLines(List<Element> lines, int n) {
     n = Math.max(0, n);
     while (lines.length > n) {
       lines.removeLast();
     }
     while (lines.length < n) {
       lines.add(new SpanElement());
     }
   }
 }