perf(various): Avoid putIfAbsent

This code was originally authored by @mhevery in the
DirectiveInjector change.

lib/change_detection/dirty_checking_change_detector.dart

@@ -1417,7 +1417,12 @@ class DuplicateMap {
   final map = new HashMap<dynamic, _DuplicateItemRecordList>();
 
   void put(ItemRecord record, [ItemRecord insertBefore = null]) {
-    map.putIfAbsent(record.item, () => new _DuplicateItemRecordList()).add(record, insertBefore);
+    var key = record.item;
+    _DuplicateItemRecordList duplicates = map[key];
+    if (duplicates == null) {
+      duplicates = map[key] = new _DuplicateItemRecordList();
+    }
+    duplicates.add(record, insertBefore);
   }
 
   /**

lib/change_detection/watch_group.dart

@@ -139,9 +139,10 @@ class WatchGroup implements _EvalWatchList, _WatchGroupList {
   }
 
   Watch watch(AST expression, ReactionFn reactionFn) {
-    WatchRecord<_Handler> watchRecord =
-        _cache.putIfAbsent(expression.expression,
-            () => expression.setupWatch(this));
+    WatchRecord<_Handler> watchRecord = _cache[expression.expression];
+    if (watchRecord == null) {
+      _cache[expression.expression] = watchRecord = expression.setupWatch(this);
+    }
     return watchRecord.handler.addReactionFn(reactionFn);
   }
 
@@ -160,8 +161,10 @@ class WatchGroup implements _EvalWatchList, _WatchGroupList {
     _fieldCost++;
     fieldHandler.watchRecord = watchRecord;
 
-    WatchRecord<_Handler> lhsWR = _cache.putIfAbsent(lhs.expression,
-        () => lhs.setupWatch(this));
+    WatchRecord<_Handler> lhsWR = _cache[lhs.expression];
+    if (lhsWR == null) {
+      lhsWR = _cache[lhs.expression] = lhs.setupWatch(this);
+    }
 
     // We set a field forwarding handler on LHS. This will allow the change
     // objects to propagate to the current WatchRecord.
@@ -177,8 +180,10 @@ class WatchGroup implements _EvalWatchList, _WatchGroupList {
     var watchRecord = _changeDetector.watch(null, null, collectionHandler);
     _collectionCost++;
     collectionHandler.watchRecord = watchRecord;
-    WatchRecord<_Handler> astWR = _cache.putIfAbsent(ast.expression,
-        () => ast.setupWatch(this));
+    WatchRecord<_Handler> astWR = _cache[ast.expression];
+    if (astWR == null) {
+      astWR = _cache[ast.expression] = ast.setupWatch(this);
+    }
 
     // We set a field forwarding handler on LHS. This will allow the change
     // objects to propagate to the current WatchRecord.
@@ -229,26 +234,32 @@ class WatchGroup implements _EvalWatchList, _WatchGroupList {
     invokeHandler.watchRecord = evalWatchRecord;
 
     if (lhsAST != null) {
-      var lhsWR = _cache.putIfAbsent(lhsAST.expression,
-          () => lhsAST.setupWatch(this));
+      var lhsWR = _cache[lhsAST.expression];
+      if (lhsWR == null) {
+        lhsWR = _cache[lhsAST.expression] = lhsAST.setupWatch(this);
+      }
       lhsWR.handler.addForwardHandler(invokeHandler);
       invokeHandler.acceptValue(lhsWR.currentValue);
     }
 
     // Convert the args from AST to WatchRecords
     for (var i = 0; i < argsAST.length; i++) {
       var ast = argsAST[i];
-      WatchRecord<_Handler> record =
-          _cache.putIfAbsent(ast.expression, () => ast.setupWatch(this));
+      WatchRecord<_Handler> record = _cache[ast.expression];
+      if (record == null) {
+        record = _cache[ast.expression] = ast.setupWatch(this);
+      }
       _ArgHandler handler = new _PositionalArgHandler(this, evalWatchRecord, i);
       _ArgHandlerList._add(invokeHandler, handler);
       record.handler.addForwardHandler(handler);
       handler.acceptValue(record.currentValue);
     }
 
     namedArgsAST.forEach((Symbol name, AST ast) {
-      WatchRecord<_Handler> record = _cache.putIfAbsent(ast.expression,
-          () => ast.setupWatch(this));
+      WatchRecord<_Handler> record = _cache[ast.expression];
+      if (record == null) {
+        record = _cache[ast.expression] = ast.setupWatch(this);
+      }
       _ArgHandler handler = new _NamedArgHandler(this, evalWatchRecord, name);
       _ArgHandlerList._add(invokeHandler, handler);
       record.handler.addForwardHandler(handler);

lib/core_dom/element_binder.dart

@@ -118,7 +118,8 @@ class ElementBinder {
 
   void _createAttrMappings(directive, scope, List<MappingParts> mappings, nodeAttrs, tasks) {
     Scope directiveScope; // Only created if there is a two-way binding in the element.
-    mappings.forEach((MappingParts p) {
+    for(var i = 0; i < mappings.length; i++) {
+      MappingParts p = mappings[i];
       var attrName = p.attrName;
       var attrValueAST = p.attrValueAST;
       AST dstAST = p.dstAST;
@@ -142,7 +143,7 @@ class ElementBinder {
         } else {
           _bindOneWay(tasks, bindAttr, scope, dstAST, directive);
         }
-        return;
+        continue;
       }
 
       switch (p.mode) {
@@ -155,7 +156,7 @@ class ElementBinder {
           break;
 
         case '<=>': // two-way
-          if (nodeAttrs[attrName] == null) return;
+          if (nodeAttrs[attrName] == null) continue;
           if (directiveScope == null) {
             directiveScope = scope.createChild(directive);
           }
@@ -164,13 +165,12 @@ class ElementBinder {
           break;
 
         case '=>': // one-way
-          if (nodeAttrs[attrName] == null) return;
-          _bindOneWay(tasks, attrValueAST, scope,
-              dstAST, directive);
+          if (nodeAttrs[attrName] == null) continue;
+          _bindOneWay(tasks, attrValueAST, scope, dstAST, directive);
           break;
 
         case '=>!': //  one-way, one-time
-          if (nodeAttrs[attrName] == null) return;
+          if (nodeAttrs[attrName] == null) continue;
 
           var watch;
           var lastOneTimeValue;
@@ -193,7 +193,7 @@ class ElementBinder {
           _bindCallback(dstAST.parsedExp, directive, nodeAttrs[attrName], scope);
           break;
       }
-    });
+    }
   }
 
   void _link(nodeInjector, probe, scope, nodeAttrs) {