pass library files not directories to analysis server

editor/tools/plugins/com.google.dart.tools.core/src/com/google/dart/tools/core/analysis/Context.java

Index: editor/tools/plugins/com.google.dart.tools.core/src/com/google/dart/tools/core/analysis/Context.java
===================================================================
--- editor/tools/plugins/com.google.dart.tools.core/src/com/google/dart/tools/core/analysis/Context.java	(revision 9145)
+++ editor/tools/plugins/com.google.dart.tools.core/src/com/google/dart/tools/core/analysis/Context.java	(working copy)
@@ -102,6 +102,12 @@
    *          <code>null</code> if none
    */
   public void parse(File libraryFile, File dartFile, ParseCallback callback) {
+    if (!libraryFile.isAbsolute()) {
+      throw new IllegalArgumentException("File path must be absolute: " + libraryFile);
+    }
+    if (libraryFile.isDirectory()) {
+      throw new IllegalArgumentException("Cannot parse a directory: " + libraryFile);
+    }
     String relPath = libraryFile.toURI().relativize(dartFile.toURI()).getPath();
     server.queueNewTask(new ParseFileTask(server, this, libraryFile, relPath, dartFile, callback));
   }
@@ -137,6 +143,9 @@
     if (!libraryFile.isAbsolute()) {
       throw new IllegalArgumentException("File path must be absolute: " + libraryFile);
     }
+    if (libraryFile.isDirectory()) {
+      throw new IllegalArgumentException("Cannot resolve a directory: " + libraryFile);
+    }
     server.queueNewTask(new AnalyzeLibraryTask(server, this, libraryFile, callback));
   }