message: Clarify error message for missing feature names
diff: @@ -292,7 +292,7 @@ function handleElement(feature: analyzer.Element, root: ts.Document) {
  parent = root;
  } else {
  - console.error('Could not find a name.');
  + console.error(`Could not find element name defined in ${feature.sourceRange}`);
  return;
  }
  @@ -367,7 +367,7 @@ function handleElement(feature: analyzer.Element, root: ts.Document) {
  */
  function handleBehavior(feature: analyzer.PolymerBehavior, root: ts.Document) {
  if (!feature.className) {
  - console.error('Could not find a name for behavior.');
  + console.error(`Could not find a name for behavior defined in ${feature.sourceRange}`);
  return;
  }
  @@ -488,7 +488,7 @@ function transitiveMixins(
  */
  function handleClass(feature: analyzer.Class, root: ts.Document) {
  if (!feature.className) {
  - console.error('Could not find a name for class.');
  + console.error(`Could not find a name for class defined in ${feature.sourceRange}`);
  return;
  }
  const [namespacePath, name] = splitReference(feature.className);
  