Implement Function.apply in vm (issue 5670).

runtime/lib/function_patch.dart

Index: runtime/lib/function_patch.dart
===================================================================
--- runtime/lib/function_patch.dart	(revision 16173)
+++ runtime/lib/function_patch.dart	(working copy)
@@ -3,9 +3,28 @@
 // BSD-style license that can be found in the LICENSE file.
 
 patch class Function {
+  static _apply(List arguments, List names)
+      native "Function_apply";
+
   /* patch */ static apply(Function function,
                            List positionalArguments,
                            [Map<String,dynamic> namedArguments]) {
-    throw new UnimplementedError('Function.apply not implemented');
+    int numPositionalArguments = 1 +  // Function is first implicit argument.
+        (positionalArguments != null ? positionalArguments.length : 0);
+    int numNamedArguments = namedArguments != null ? namedArguments.length : 0;
+    int numArguments = numPositionalArguments + numNamedArguments;
+    List arguments = new List(numArguments);
+    arguments[0] = function;
+    arguments.setRange(1, numPositionalArguments - 1, positionalArguments);
+    List names = new List(numNamedArguments);
+    int argumentIndex = numPositionalArguments;
+    int nameIndex = 0;
+    if (numNamedArguments > 0) {
+      namedArguments.forEach((name, value) {
+        arguments[argumentIndex++] = value;
+        names[nameIndex++] = name;
+      });
+    }
+    return _apply(arguments, names);
   }
 }