fix support for --package-root command line option to analyzer dartbug.com/4225

compiler/java/com/google/dart/compiler/DefaultCompilerConfiguration.java

Index: compiler/java/com/google/dart/compiler/DefaultCompilerConfiguration.java
===================================================================
--- compiler/java/com/google/dart/compiler/DefaultCompilerConfiguration.java	(revision 9979)
+++ compiler/java/com/google/dart/compiler/DefaultCompilerConfiguration.java	(working copy)
@@ -14,6 +14,7 @@
 import java.net.URI;
 import java.net.URISyntaxException;
 import java.util.ArrayList;
+import java.util.Arrays;
 import java.util.List;
 
 /**
@@ -27,6 +28,7 @@
 
   private final SystemLibraryManager systemLibraryManager;
 
+
   /**
    * A default configuration.
    */
@@ -50,6 +52,7 @@
     this.compilerOptions = compilerOptions;
     this.compilerMetrics = compilerOptions.showMetrics() ? new CompilerMetrics() : null;
     this.systemLibraryManager = libraryManager;
+    systemLibraryManager.setPackageRoots(Arrays.asList(new File[]{compilerOptions.getPackageRoot()}));
   }
 
   @Override
@@ -123,7 +126,7 @@
 
     return new UrlLibrarySource(systemUri, this.systemLibraryManager);
   }
-
+  
   @Override
   public CompilerOptions getCompilerOptions() {
     return compilerOptions;
@@ -133,4 +136,9 @@
   public ErrorFormat printErrorFormat() {
     return compilerOptions.printErrorFormat();
   }
+  
+  @Override
+  public SystemLibraryManager getSystemLibraryManager() {
+    return systemLibraryManager;
+  }
 }