A couple utility methods

PsiCodegenPredictor.getFileForCodegenNamedClass() returns JetFile which
contains a declaration which will produce a class with a given name.
PsiCodegenPredictor.getFileForNamespacePartName() returns JetFile which
produces a namespace part with the given name.

BindingContextUtils.getContainingFile() returns JetFile which contains a
declaration which is matched to a given descriptor.

DescriptorUtils.findTopLevelParent() finds a top-level (i.e. its containing
declaration is NamespaceDescriptor) parent for a descriptor.

Also DescriptorUtils.isTopLevelFunction() is changed a little to accept not
only a function, but any descriptor

idea/src/org/jetbrains/jet/plugin/completion/handlers/JetFunctionInsertHandler.java

@@ -187,7 +187,7 @@ public class JetFunctionInsertHandler implements InsertHandler<LookupElement> {
                             return;
                         }
 
-                        if (DescriptorUtils.isTopLevelFunction(functionDescriptor)) {
+                        if (DescriptorUtils.isTopLevelDeclaration(functionDescriptor)) {
                             ApplicationManager.getApplication().runWriteAction(new Runnable() {
                                 @Override
                                 public void run() {