Allow an AJAX call to specify that it should not notify on error

Because there are some cases where it's OK to fail, and it's not the user's fault

cms/static/coffee/src/main.coffee

@@ -16,6 +16,8 @@ $ ->
     dataType: 'json'
 
   $(document).ajaxError (event, jqXHR, ajaxSettings, thrownError) ->
+    if ajaxSettings.notifyOnError is false
+      return
     msg = new CMS.Models.ErrorMessage(
         "title": gettext("Studio's having trouble saving your work")
         "message": jqXHR.responseText || gettext("This may be happening because of an error with our server or your internet connection. Try refreshing the page or making sure you are online.")

common/lib/xmodule/xmodule/js/src/video/display/video_caption.coffee

@@ -27,16 +27,19 @@ class @VideoCaption extends Subview
     @fetchCaption()
 
   fetchCaption: ->
-    $.getWithPrefix @captionURL(), (captions) =>
-      @captions = captions.text
-      @start = captions.start
-
-      @loaded = true
-
-      if onTouchBasedDevice()
-        $('.subtitles li').html "Caption will be displayed when you start playing the video."
-      else
-        @renderCaption()
+    $.ajaxWithPrefix
+      url: @captionURL()
+      notifyOnError: false
+      success: (captions) =>
+        @captions = captions.text
+        @start = captions.start
+
+        @loaded = true
+
+        if onTouchBasedDevice()
+          $('.subtitles li').html "Caption will be displayed when you start playing the video."
+        else
+          @renderCaption()
 
   renderCaption: ->
     container = $('<ol>')

common/lib/xmodule/xmodule/js/src/videoalpha/display/video_caption.coffee

@@ -27,16 +27,19 @@ class @VideoCaptionAlpha extends SubviewAlpha
     @fetchCaption()
 
   fetchCaption: ->
-    $.getWithPrefix @captionURL(), (captions) =>
-      @captions = captions.text
-      @start = captions.start
-
-      @loaded = true
-
-      if onTouchBasedDevice()
-        $('.subtitles li').html "Caption will be displayed when you start playing the video."
-      else
-        @renderCaption()
+    $.ajaxWithPrefix
+      url: @captionURL()
+      notifyOnError: false
+      success: (captions) =>
+        @captions = captions.text
+        @start = captions.start
+
+        @loaded = true
+
+        if onTouchBasedDevice()
+          $('.subtitles li').html "Caption will be displayed when you start playing the video."
+        else
+          @renderCaption()
 
   renderCaption: ->
     container = $('<ol>')