Fix to dartbug.com/5170, explictly static library variables now get an appropriate error message.

lib/compiler/implementation/tree/nodes.dart

Index: lib/compiler/implementation/tree/nodes.dart
diff --git a/lib/compiler/implementation/tree/nodes.dart b/lib/compiler/implementation/tree/nodes.dart
index 72467acf9edb737f639d35ab13a9a95ef5871f0a..c31df5a2a4c1d9d279d96eb42fc74cbecb2bcb78 100644
--- a/lib/compiler/implementation/tree/nodes.dart
+++ b/lib/compiler/implementation/tree/nodes.dart
@@ -1171,6 +1171,17 @@ class Modifiers extends Node {
     }
     return flags;
   }
+  
+  Node findModifier(String modifier) {
+    Link<Node> nodeList = nodes.nodes;
+    for (; !nodeList.isEmpty(); nodeList = nodeList.tail) {
+      String value = nodeList.head.asIdentifier().source.stringValue;
+      if(value === modifier) {
+        return nodeList.head;
+      }
+    }
+    return null;
+  }
 
   Modifiers asModifiers() => this;
   Token getBeginToken() => nodes.getBeginToken();
@@ -1186,6 +1197,8 @@ class Modifiers extends Node {
   bool isFactory() => (flags & FLAG_FACTORY) != 0;
   bool isExternal() => (flags & FLAG_EXTERNAL) != 0;
 
+  Node getStatic() => findModifier('static');
+
   /**
    * Use this to check if the declaration is either explicitly or implicitly
    * final.