[Extension API Extern Generation] Fix a few bugs in extern generation

tools/json_schema_compiler/js_externs_generator_test.py

Index: tools/json_schema_compiler/js_externs_generator_test.py
diff --git a/tools/json_schema_compiler/js_externs_generator_test.py b/tools/json_schema_compiler/js_externs_generator_test.py
index 004b79c1f8d9c457dbe4aabc8672dd29577a3458..b74260daf86e5fcc0932bdd79b6501d651356fe6 100755
--- a/tools/json_schema_compiler/js_externs_generator_test.py
+++ b/tools/json_schema_compiler/js_externs_generator_test.py
@@ -43,6 +43,7 @@ namespace fakeApi {
     Bar obj;
     long? maybe;
     (DOMString or Greek or long[]) choice;
+    object plainObj;
   };
 
   callback VoidCallback = void();
@@ -114,7 +115,8 @@ var Bar;
  *   anythingGoes: !Array<*>,
  *   obj: Bar,
  *   maybe: (number|undefined),
- *   choice: (string|!chrome.fakeApi.Greek|!Array<number>)
+ *   choice: (string|!chrome.fakeApi.Greek|!Array<number>),
+ *   plainObj: Object
  * }}
  * @see https://developer.chrome.com/extensions/fakeApi#type-Baz
  */