Code generation for extensions api

tools/json_schema_compiler/test/windows.json

 [
   {
     "namespace": "windows",
+    "generate": true,
     "types": [
       {
         "id": "Window",
         "type": "object",
         "properties": {
           "id": {"type": "integer", "minimum": 0, "description": "The ID of the window. Window IDs are unique within a browser session."},
           "focused": {"type": "boolean", "description": "Whether the window is currently the focused window."},
           "top": {"type": "integer", "description": "The offset of the window from the top edge of the screen in pixels."},
           "left": {"type": "integer", "description": "The offset of the window from the left edge of the screen in pixels."},
           "width": {"type": "integer", "description": "The width of the window in pixels."},
@@ skipping 240 matching lines @@
         "name": "onFocusChanged",
         "type": "function",
         "description": "Fired when the currently focused window changes. Will be chrome.windows.WINDOW_ID_NONE if all chrome windows have lost focus. Note: On some Linux window managers, WINDOW_ID_NONE will always be sent immediately preceding a switch from one chrome window to another.",
         "parameters": [
           {"type": "integer", "name": "windowId", "minimum": -1, "description": "ID of the newly focused window."}
         ]
       }
     ]
   }
 ]