Make edxnotes bok-choy tests chrome-friendly.

This eliminates some flakiness related to the loading of the notes page. It also
sets the 'no content' version of that page as a separate page object so testing
that case is more explicit.

TE-849

common/test/acceptance/pages/lms/edxnotes.py

@@ -201,7 +201,7 @@ class EdxNotesPage(CoursePage):
         self.current_view = self.MAPPING["recent"](self.browser)
 
     def is_browser_on_page(self):
-        return self.q(css=".wrapper-student-notes").present
+        return self.q(css=".wrapper-student-notes .note-group").visible
 
     def switch_to_tab(self, tab_name):
         """
@@ -282,6 +282,16 @@ class EdxNotesPage(CoursePage):
         children = self.q(css='.note-section')
         return [EdxNotesPageSection(self.browser, child.get_attribute("id")) for child in children]
 
+
+class EdxNotesPageNoContent(CoursePage):
+    """
+    EdxNotes page -- when no notes have been added.
+    """
+    url_path = "edxnotes/"
+
+    def is_browser_on_page(self):
+        return self.q(css=".wrapper-student-notes .is-empty").visible
+
     @property
     def no_content_text(self):
         """

common/test/acceptance/tests/lms/test_lms_edxnotes.py

@@ -6,7 +6,7 @@ from ...fixtures.course import CourseFixture, XBlockFixtureDesc
 from ...pages.lms.auto_auth import AutoAuthPage
 from ...pages.lms.course_nav import CourseNavPage
 from ...pages.lms.courseware import CoursewarePage
-from ...pages.lms.edxnotes import EdxNotesUnitPage, EdxNotesPage
+from ...pages.lms.edxnotes import EdxNotesUnitPage, EdxNotesPage, EdxNotesPageNoContent
 from ...fixtures.edxnotes import EdxNotesFixture, Note, Range
 
 
@@ -413,10 +413,11 @@ class EdxNotesPageTest(EdxNotesTestMixin):
         When I open Notes page
         Then I see only "You do not have any notes within the course." message
         """
-        self.notes_page.visit()
+        notes_page_empty = EdxNotesPageNoContent(self.browser, self.course_id)
+        notes_page_empty.visit()
         self.assertIn(
             "You have not made any notes in this course yet. Other students in this course are using notes to:",
-            self.notes_page.no_content_text)
+            notes_page_empty.no_content_text)
 
     def test_recent_activity_view(self):
         """