Chrome Version       : 70.0.3538.16
OS Version: Chrome

What steps will reproduce the problem?
1. Get a corrupt thumbnail

What is the expected result?

Have some idea about what was wrong.


What happens instead of that?

Even running with `buildr chrome --show-component-extension-options` and inspecting the background page of the image loader extension to look at the console log often isn't sufficient.


Plumbed throughout image_loader.js / request.js are calls to `onFailure()` -- no arguments are passed. I think we should pass an error code that can be surfaced in UI. And, to begin with, a US-English error description sent to console.log in the foreground app (not image_loader).

Eventually, we could surface the error, translated, as a tooltip, or do some other UX.


Some possible errors I've encountered:

 - Loading RAW images is not supported unless build_type = Official (silent failure)

 - Video thumbnails failing with 'MEDIA_ERR_SRC_NOT_SUPPORTED' (4)
   - this surfaces in ImageRequest.prototype.downloadOriginal_, when it catches an error thrown by createVideoThumbnailUrl -- error.type is `error` error.target is <video> error.path[0].error is 'MediaError', MediaError.code is 4, MediaError.message is "MEDIA_ELEMENT_ERROR: Empty src attribute"

 - Sony "arw" files are not loading (even in Official) - still diagnosing this one...