Check that interface constructors and default class constructors are compatible.

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

Index: compiler/java/com/google/dart/compiler/resolver/ConstructorElementImplementation.java
diff --git a/compiler/java/com/google/dart/compiler/resolver/ConstructorElementImplementation.java b/compiler/java/com/google/dart/compiler/resolver/ConstructorElementImplementation.java
index e5ad047570d00deea5625bd766a6ec472a2011a2..9f4a96ad32e62d21cdf99871f21430df66e140b8 100644
--- a/compiler/java/com/google/dart/compiler/resolver/ConstructorElementImplementation.java
+++ b/compiler/java/com/google/dart/compiler/resolver/ConstructorElementImplementation.java
@@ -10,6 +10,7 @@ import com.google.dart.compiler.ast.Modifiers;
 class ConstructorElementImplementation extends MethodElementImplementation
     implements ConstructorElement {
   private final ClassElement constructorType;
+  private ConstructorElement defaultConstructor;
 
   private ConstructorElementImplementation(DartMethodDefinition node,
                              String name,
@@ -40,6 +41,16 @@ class ConstructorElementImplementation extends MethodElementImplementation
     return true;
   }
 
+  @Override
+  public ConstructorElement getDefaultConstructor() {
+    return defaultConstructor;
+  }
+
+  @Override
+  public void setDefaultConstructor(ConstructorElement defaultConstructor) {
+    this.defaultConstructor = defaultConstructor;
+  }
+
   public static ConstructorElementImplementation fromMethodNode(DartMethodDefinition node,
                                                   String name,
                                                   ClassElement declaringClass,