Issue 1548. If URI can not be parsed, return null.

compiler/java/com/google/dart/compiler/UrlLibrarySource.java

Index: compiler/java/com/google/dart/compiler/UrlLibrarySource.java
diff --git a/compiler/java/com/google/dart/compiler/UrlLibrarySource.java b/compiler/java/com/google/dart/compiler/UrlLibrarySource.java
index c5b6992e1316b6de8a1aeedcf568b26d06b4db1d..6f5c83e817316cc63e033553875363005f5d6fbc 100644
--- a/compiler/java/com/google/dart/compiler/UrlLibrarySource.java
+++ b/compiler/java/com/google/dart/compiler/UrlLibrarySource.java
@@ -1,18 +1,15 @@
 // Copyright (c) 2011, 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;
 
 import java.io.File;
 import java.net.URI;
-import java.net.URISyntaxException;
 
 /**
  * A {@link LibrarySource} backed by a URL.
  */
 public class UrlLibrarySource extends UrlSource implements LibrarySource {
-
   public UrlLibrarySource(URI uri, SystemLibraryManager slm) {
     super(uri, slm);
   }
@@ -36,13 +33,17 @@ public class UrlLibrarySource extends UrlSource implements LibrarySource {
       // Force the creation of an escaped relative URI to deal with spaces, etc.
       URI uri = getUri().resolve(new URI(null, null, relPath, null)).normalize();
       return new UrlDartSource(uri, relPath, this, systemLibraryManager);
-    } catch (URISyntaxException e) {
-      throw new AssertionError(e);
+    } catch (Throwable e) {
+      return null;
     }
   }
 
   @Override
   public LibrarySource getImportFor(String relPath) {
-    return new UrlLibrarySource(getUri().resolve(relPath).normalize(), systemLibraryManager);
+    try {
+      return new UrlLibrarySource(getUri().resolve(relPath).normalize(), systemLibraryManager);
+    } catch (Throwable e) {
+      return null;
+    }
   }
 }