Addresses a ClassCastException seen in the editor from MemberBuilder

compiler/java/com/google/dart/compiler/resolver/MemberBuilder.java

Index: compiler/java/com/google/dart/compiler/resolver/MemberBuilder.java
diff --git a/compiler/java/com/google/dart/compiler/resolver/MemberBuilder.java b/compiler/java/com/google/dart/compiler/resolver/MemberBuilder.java
index d9a28b777df87740b7dc81a40afb74aaca5b658d..f99cd9ecaceb8ba689a034b6115fb091aae61431 100644
--- a/compiler/java/com/google/dart/compiler/resolver/MemberBuilder.java
+++ b/compiler/java/com/google/dart/compiler/resolver/MemberBuilder.java
@@ -180,8 +180,7 @@ public class MemberBuilder {
             return Elements.constructorFromMethodNode(
                 method, node.getPropertyName(), (ClassElement) currentHolder, (ClassElement) element);
           } else {
-            topLevelContext.internalError(node,
-                "Library prefixes not implemented yet");
+            // Nothing else is valid. Already warned in getMethodKind().
             return getTypeProvider().getDynamicType().getElement();
           }
         }
@@ -387,12 +386,17 @@ public class MemberBuilder {
         }
       } else {
         DartPropertyAccess property = (DartPropertyAccess) name;
-        DartIdentifier qualifier = (DartIdentifier) property.getQualifier();
-        if (qualifier.getTargetName().equals(currentHolder.getName())) {
-          return ElementKind.CONSTRUCTOR;
-        } else {
+        if (property.getQualifier() instanceof DartIdentifier) {
+          DartIdentifier qualifier = (DartIdentifier) property.getQualifier();
+          if (qualifier.getTargetName().equals(currentHolder.getName())) {
+            return ElementKind.CONSTRUCTOR;
+          }
           resolutionError(method.getName(),
                           ResolverErrorCode.CANNOT_DECLARE_NON_FACTORY_CONSTRUCTOR);
+        } else {
+          // Multiple qualifiers (Foo.bar.baz)
+          resolutionError(method.getName(),
+                          ResolverErrorCode.TOO_MANY_QUALIFIERS_FOR_METHOD);
         }
       }