When an HTMLImageElement's 'src' is set to the empty string, the state
of the image request will be 'broken', and thus the promise should be
rejected with an InvalidStateError exception per the rules at [1].

Move the intrinsic size check below the image existence check, and use
a more direct method of getting at the size (no need to go through the
BitmapImageSource interface when we're already fiddling with internals).

Also add a check for IsLoaded() to better match the spec wording
'fully decodable'.

[1] https://wicg.github.io/shape-detection-api/#image-sources-for-detection

Bug: 789511
Change-Id: I69ac4a9081cfff7f9c7c8f7edf39667e3dd1eb4d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2587165


Reviewed-by: Reilly Grant <reillyg@chromium.org>
Commit-Queue: Fredrik Söderquist <fs@opera.com>
Cr-Commit-Position: refs/heads/master@{#837140}