Reapply "Make patch file import declarations apply to the patched library too."

lib/compiler/implementation/elements/elements.dart

 // Copyright (c) 2012, 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('elements');
 
 #import('../tree/tree.dart');
 #import('../scanner/scannerlib.dart');
 #import('../leg.dart');  // TODO(karlklose): we only need type.
 #import('../util/util.dart');
@@ skipping 368 matching lines @@
       // Use the file name as script name.
       var path = script.uri.path;
       return path.substring(path.lastIndexOf('/') + 1);
     }
   }
 }
 
 class PrefixElement extends Element {
   Map<SourceString, Element> imported;
   Token firstPosition;
+  final CompilationUnitElement patchSource;
 
-  PrefixElement(SourceString prefix, Element enclosing, this.firstPosition)
+  PrefixElement(SourceString prefix, Element enclosing, this.firstPosition,
+                [this.patchSource])
     : imported = new Map<SourceString, Element>(),
       super(prefix, ElementKind.PREFIX, enclosing);
 
+  CompilationUnitElement getCompilationUnit() {
+    if (patchSource !== null) return patchSource;
+    return super.getCompilationUnit();
+  }
+
   lookupLocalMember(SourceString memberName) => imported[memberName];
 
   Type computeType(Compiler compiler) => compiler.types.dynamicType;
 
   Token position() => firstPosition;
 }
 
 class TypedefElement extends Element {
   Type cachedType;
   Typedef cachedNode;
@@ skipping 725 matching lines @@
   final Node node;
   Type bound;
   Type type;
   TypeVariableElement(name, Element enclosing, this.node, this.type,
                       [this.bound])
     : super(name, ElementKind.TYPE_VARIABLE, enclosing);
   Type computeType(compiler) => type;
   Node parseNode(compiler) => node;
   toString() => "${enclosingElement.toString()}.${name.slowToString()}";
 }