Make sure the canvas is always the first child of its wrapper

[calixteman]

While drawing, in zooming fast enough, it's possible, intermittently, to have the canvas after the svg which makes the svg invisible.
So this patch makes sure to have the canvas at the right position.

[calixteman]

/botio integrationtest

[moz-tools-bot]

From: Bot.io (Windows)

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Received

Command cmd_integrationtest from @calixteman received. Current queue size: 0

Live output at: http://54.193.163.58:8877/fd2a2c230e44f8e/output.txt

[moz-tools-bot]

From: Bot.io (Linux m4)

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Received

Command cmd_integrationtest from @calixteman received. Current queue size: 0

Live output at: http://54.241.84.105:8877/d77d5c374b7c8f5/output.txt

[Snuffleupagus]

it's possible, intermittently, to have the canvas after the svg which makes the svg invisible.

Sorry, but what SVG is this referring to since I don't believe that the canvasWrapper has any SVG elements?

[moz-tools-bot]

From: Bot.io (Linux m4)

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Success

Full output at http://54.241.84.105:8877/d77d5c374b7c8f5/output.txt

Total script time: 9.49 mins

• Integration Tests: Passed

[moz-tools-bot]

From: Bot.io (Windows)

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Failed

Full output at http://54.193.163.58:8877/fd2a2c230e44f8e/output.txt

Total script time: 24.08 mins

• Integration Tests: FAILED

[calixteman]

it's possible, intermittently, to have the canvas after the svg which makes the svg invisible.

Sorry, but what SVG is this referring to since I don't believe that the canvasWrapper has any SVG elements?

The drawings (highlights and inks) are under the canvasWrapper:

The goal of having highlights there was to make sure the blend operation was applied with the canvas as the backdrop.

[Snuffleupagus]

r=me, thank you.