PPAPI Examples: Fix painting in Graphics 2D example.

PPAPI Examples: Fix painting in Graphics 2D example.

Releasing the Graphics2D at the end of the Repaint method causes the blue image to never be visible to anyone who runs the 2d.html example. (At least on Linux)

This saves the created Graphics 2D, saves it, and releases it when the plugin instance is destroyed.

BUG=

Committed: https://crrev.com/a1b9fb3524473610a204e2c39ecd681f67d3db20
Cr-Commit-Position: refs/heads/master@{#324059}

[tommycli, 2015-04-06 22:59:24]

tommycli@chromium.org changed reviewers:
+ dmichael@chromium.org

[tommycli, 2015-04-06 22:59:48]

dmichael: PTAL

Not sure if I'm misunderstanding Graphics2D, but it wasn't working on my machine
until I made these changes.

[dmichael (off chromium), 2015-04-07 15:33:13]

What a weird old example! It probably worked 4-5 years ago in the in-process
mode or something.

lgtm, thanks for fixing it.

https://codereview.chromium.org/1065733003/diff/40001/ppapi/examples/2d/graph...
File ppapi/examples/2d/graphics_2d_example.c (left):

https://codereview.chromium.org/1065733003/diff/40001/ppapi/examples/2d/graph...
ppapi/examples/2d/graphics_2d_example.c:95:
PP_MakeCompletionCallback(&FlushCompletionCallback, NULL));
Yeah, in the old version there's no guarantee the Flush will complete since the
Graphics2D is destroyed here. And the callback should get "PP_ERROR_ABORTED" in
this case.

[tommycli, 2015-04-07 16:20:02]

The CQ bit was checked by tommycli@chromium.org

[commit-bot: I haz the power, 2015-04-07 16:20:20]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1065733003/40001

[commit-bot: I haz the power, 2015-04-07 16:59:04]

Committed patchset #3 (id:40001)

[commit-bot: I haz the power, 2015-04-07 17:01:27]

Patchset 3 (id:??) landed as
https://crrev.com/a1b9fb3524473610a204e2c39ecd681f67d3db20
Cr-Commit-Position: refs/heads/master@{#324059}