Ensure contentId is not null when creating a SourceFileCompilationUnit

Patch by: stephen.haberman
Review by: zundel
Review at: http://gwt-code-reviews.appspot.com/1463803/


git-svn-id: https://google-web-toolkit.googlecode.com/svn/trunk@10378 8db76d5a-ed1c-0410-87a9-c151d255dfc7
diff --git a/dev/core/src/com/google/gwt/dev/javac/CompilationUnitBuilder.java b/dev/core/src/com/google/gwt/dev/javac/CompilationUnitBuilder.java
index 48986cd..5ecf676 100644
--- a/dev/core/src/com/google/gwt/dev/javac/CompilationUnitBuilder.java
+++ b/dev/core/src/com/google/gwt/dev/javac/CompilationUnitBuilder.java
@@ -151,7 +151,7 @@
         List<JDeclaredType> types, Dependencies dependencies,
         Collection<? extends JsniMethod> jsniMethods, MethodArgNamesLookup methodArgs,
         CategorizedProblem[] problems) {
-      return new SourceFileCompilationUnit(getResource(), contentId, compiledClasses, types,
+      return new SourceFileCompilationUnit(getResource(), getContentId(), compiledClasses, types,
           dependencies, jsniMethods, methodArgs, problems, getLastModified());
     }
   }