Fix Studio to gracefully handle xblock JavaScript errors

TNL-46

I've changed Studio to catch JavaScript errors when rendering xblocks, log the error, but to then continue as normal. This means that the user is still able to interact with the xblock to delete, duplicate etc. This seems reasonable as the xblock is only rendered as a WYSIWYG representation so if it isn't fully interactive that shouldn't be a big problem.

common/test/acceptance/pages/studio/container.py

@@ -37,6 +37,10 @@ class ContainerPage(PageObject):
             return None
 
     def is_browser_on_page(self):
+        def _xblock_count(class_name, request_token):
+            return len(self.q(css='{body_selector} .xblock.{class_name}[data-request-token="{request_token}"]'.format(
+                body_selector=XBlockWrapper.BODY_SELECTOR, class_name=class_name, request_token=request_token
+            )).results)
 
         def _is_finished_loading():
             is_done = False
@@ -46,11 +50,15 @@ class ContainerPage(PageObject):
                 request_token = data_request_elements.first.attrs('data-request-token')[0]
                 # Then find the number of Studio xblock wrappers on the page with that request token.
                 num_wrappers = len(self.q(css='{} [data-request-token="{}"]'.format(XBlockWrapper.BODY_SELECTOR, request_token)).results)
-                # Wait until all components have been loaded.
-                # See common/static/coffee/src/xblock/core.coffee which adds the
-                # class "xblock-initialized" at the end of initializeBlock
-                num_xblocks_init = len(self.q(css='{} .xblock.xblock-initialized[data-request-token="{}"]'.format(XBlockWrapper.BODY_SELECTOR, request_token)).results)
-                is_done = num_wrappers == num_xblocks_init
+                # Wait until all components have been loaded and marked as either initialized or failed.
+                # See:
+                #   - common/static/coffee/src/xblock/core.coffee which adds the class "xblock-initialized"
+                #     at the end of initializeBlock.
+                #   - common/static/js/views/xblock.js which adds the class "xblock-initialization-failed"
+                #     if the xblock threw an error while initializing.
+                num_initialized_xblocks = _xblock_count('xblock-initialized', request_token)
+                num_failed_xblocks = _xblock_count('xblock-initialization-failed', request_token)
+                is_done = num_wrappers == (num_initialized_xblocks + num_failed_xblocks)
             return (is_done, is_done)
 
         # First make sure that an element with the view-container class is present on the page,

common/test/acceptance/tests/test_studio_bad_data.py

@@ -95,8 +95,7 @@ class JSErrorBadContentTest(BadComponentTest):
     """
     Tests that components that throw JS errors do not break the Unit page.
     """
-    # TODO: ENABLE TEST WITH ANDY'S PR
-    __test__ = False
+    __test__ = True
 
     def get_bad_html_content(self):
         """