Issue 2693. Don't add null imports

compiler/javatests/com/google/dart/compiler/end2end/inc/MemoryLibrarySource.java

Index: compiler/javatests/com/google/dart/compiler/end2end/inc/MemoryLibrarySource.java
diff --git a/compiler/javatests/com/google/dart/compiler/end2end/inc/MemoryLibrarySource.java b/compiler/javatests/com/google/dart/compiler/end2end/inc/MemoryLibrarySource.java
index b6c2cd3a25bd91dba81c3ad55bbb4069eaaac19f..8b221e725d40f6c99e65ec3f2b427cda4e83d1b7 100644
--- a/compiler/javatests/com/google/dart/compiler/end2end/inc/MemoryLibrarySource.java
+++ b/compiler/javatests/com/google/dart/compiler/end2end/inc/MemoryLibrarySource.java
@@ -1,4 +1,4 @@
-// Copyright (c) 2011, the Dart project authors. Please see the AUTHORS file
+// 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.
 package com.google.dart.compiler.end2end.inc;
@@ -8,25 +8,32 @@ import com.google.dart.compiler.DartSource;
 import com.google.dart.compiler.LibrarySource;
 import com.google.dart.compiler.Source;
 import com.google.dart.compiler.UrlDartSource;
-import com.google.dart.compiler.UrlLibrarySource;
 
 import java.io.IOException;
 import java.io.Reader;
 import java.io.StringReader;
 import java.net.URI;
-import java.net.URISyntaxException;
 import java.util.Map;
 
 /**
  * {@link LibrarySource} which provides content for all {@link Source}s from memory.
  */
 public class MemoryLibrarySource implements LibrarySource {
+  public static final String IO_EXCEPTION_CONTENT = "simulate-IOException";
   private final String libName;
-  private final Map<String, String> sourceContentMap = Maps.newHashMap();
-  private final Map<String, Long> sourceLastModifiedMap = Maps.newHashMap();
+  private final Map<String, String> sourceContentMap;
+  private final Map<String, Long> sourceLastModifiedMap;
 
-  public MemoryLibrarySource(String libName) throws URISyntaxException {
+  public MemoryLibrarySource(String libName) {
     this.libName = libName;
+    sourceContentMap = Maps.newHashMap();
+    sourceLastModifiedMap = Maps.newHashMap();
+  }
+
+  private MemoryLibrarySource(String libName, MemoryLibrarySource parent) {
+    this.libName = libName;
+    sourceContentMap = parent.sourceContentMap;
+    sourceLastModifiedMap = parent.sourceLastModifiedMap;
   }
 
   @Override
@@ -57,35 +64,15 @@ public class MemoryLibrarySource implements LibrarySource {
   @Override
   public Reader getSourceReader() throws IOException {
     String content = sourceContentMap.get(libName);
+    if (IO_EXCEPTION_CONTENT.equals(content)) {
+      throw new IOException("simulated");
+    }
     return new StringReader(content);
   }
 
   @Override
   public LibrarySource getImportFor(final String relPath) throws IOException {
-    final String content = sourceContentMap.get(relPath);
-    final Long sourceLastModified = sourceLastModifiedMap.get(relPath);
-    URI uri = URI.create(relPath);
-    return new UrlLibrarySource(uri) {
-      @Override
-      public boolean exists() {
-        return content != null;
-      }
-
-      @Override
-      public long getLastModified() {
-        return sourceLastModified.longValue();
-      }
-
-      @Override
-      public Reader getSourceReader() throws IOException {
-        return new StringReader(content);
-      }
-
-      @Override
-      public DartSource getSourceFor(String relPath) {
-        return MemoryLibrarySource.this.getSourceFor(relPath);
-      }
-    };
+    return new MemoryLibrarySource(relPath, this);
   }
 
   @Override