1286731 - Return correct DrawResult from nsCSSRendering::PaintBackgroundWithSC

Status: NEW

(Core :: Layout, defect, P3)

Description

[u459114]

nsCSSRendering::PaintBackgroundWithSC calls DrawBackground at [1], and store the drawing result in 'result' variable by "&=" operator, which I think is not correct.

Let's said we have 2 background images need to be drawn:
The fist background image is not decoded complete yet, then we will get result to be set as DrawResult::NOT_READY now.
Next, we start to draw the second background image, and this image is ready to draw, so 'result' is overwrite as DrawResult::SUCCESS. The caller of PaintBackgroundWithSC have no idea that we still have an image is not drawn correctly yet.

I propose 
1. Change DrawResult to bit field, so that we can store more information in it.
2. Change "&=" operator at [1] to "|=" operator.

[1] https://dxr.mozilla.org/mozilla-central/source/layout/base/nsCSSRendering.cpp#3123

Comment 1

[Timothy Nikkel (:tnikkel)]

DrawResult overloads the & operator

https://dxr.mozilla.org/mozilla-central/source/image/DrawResult.h

so wouldn't the result of

  NOT_READY & SUCCESS

be NOT_READY?