Make unsafecast static.

Change-Id: Iab6d87b5642456c2fa10f91209a00fcba9e8d018
diff --git a/user/super/com/google/gwt/emul/java/lang/Boolean.java b/user/super/com/google/gwt/emul/java/lang/Boolean.java
index e3e885f..fee3759 100644
--- a/user/super/com/google/gwt/emul/java/lang/Boolean.java
+++ b/user/super/com/google/gwt/emul/java/lang/Boolean.java
@@ -98,7 +98,7 @@
     return unsafeCast(checkNotNull(this));
   }
 
-  private native boolean unsafeCast(Object value) /*-{
+  private static native boolean unsafeCast(Object value) /*-{
     return value;
   }-*/;
 
diff --git a/user/super/com/google/gwt/emul/java/lang/Double.java b/user/super/com/google/gwt/emul/java/lang/Double.java
index 67ff44d..13f0216 100644
--- a/user/super/com/google/gwt/emul/java/lang/Double.java
+++ b/user/super/com/google/gwt/emul/java/lang/Double.java
@@ -312,7 +312,7 @@
     return unsafeCast(checkNotNull(this));
   }
 
-  private native double unsafeCast(Object instance) /*-{
+  private static native double unsafeCast(Object instance) /*-{
     return instance;
   }-*/;