[web] Fix canvas leak when dpi changes. Evict from BitmapCanvas cache under…

[ferhatb]

Prevents very small recordings using large canvas(s).
When BitmapCanvas cache is full and canvas allocation fails on iOS devices, empty cache and retry.
Change drawColor to utilize DomCanvas instead of screen size BitmapCanvas allocation.
Optimize drawPath for simple rect and roundrect paths.

[harryterkelsen]

Comment seems inaccurate. It looks like we're actually deleting all of the recycled canvases.

Maybe this would be a little faster with:

for (int i = 0; i < canvasCount; i++) {
  _recycledCanvases[i].dispose();
}
_recycledCanvases.clear();

[ferhatb]

thx. done.

[yjbanov]

But, is this function used anywhere? :)

[harryterkelsen]

waiting for what?

[yjbanov]

Let's add tests for these changes.

[yjbanov]

But, is this function used anywhere? :)

[yjbanov]

Let's rename the variable to isCanvasTooBig. Otherwise, the distinction between isSmaller and isTooSmall is unclear.

[yjbanov]

I would also move this computation inside the if block, because if the canvas doesn't fit or is not smaller that the previous canvas, then this computation has no effect (you'd also be able to remove the isSmaller from this expression).

[yjbanov]

Are we ok picking up canvases that are 10x bigger than the picture?

[yjbanov]

We can get NaN in maxPaintBounds (see https://github.com/flutter/engine/blob/master/lib/web_ui/lib/src/engine/surface/recording_canvas.dart#L1887)

[ferhatb]

reverted change.