Clear m_lastImageId for software compositor

Clear m_lastImageId for software compositor

When android webview swith to software only mode, all mailboxes are
returned to Canvas2DLayerBridge. In this case, if the canvas is static,
then prepareMailbox will never return a new mailbox. So clear m_lastImageId
in this case.

BUG=239864
Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=167365

[boliu, 2014-02-14 21:35:26]

A much simpler solution to the android webview static canvas issue. PTAL!

[boliu, 2014-02-18 15:14:35]

junov: ping?

[Justin Novosad, 2014-02-18 16:47:22]

On 2014/02/18 15:14:35, boliu wrote:
> junov: ping?

Is there a test for this?

Are we sure this is enough?  Is it possible for the the compositor to switch to
software compositing and come back to hardware compositing without ever having
called prepareMailbox?  We may need more work to handle that case.

[boliu, 2014-02-18 16:51:21]

On 2014/02/18 16:47:22, junov wrote:
> On 2014/02/18 15:14:35, boliu wrote:
> > junov: ping?
> 
> Is there a test for this?
> 

Sure I can add one. Probably something simple since I can't mock out the
context.

> Are we sure this is enough?  Is it possible for the the compositor to switch
to
> software compositing and come back to hardware compositing without ever having
> called prepareMailbox?  We may need more work to handle that case.

That should not be possible as they are post tasks back to the main thread and
will be handled in order. Also that would be a bug in the compositor rather than
here imo.

[boliu, 2014-02-18 17:15:01]

Added a tiny unit test. PTAL

[Justin Novosad, 2014-02-18 17:51:46]

On 2014/02/18 17:15:01, boliu wrote:
> Added a tiny unit test. PTAL

lgtm

Since the test is under Source/web, you need approval from someone who is an
owner there too :-(

[boliu, 2014-02-18 17:56:24]

+aelias for Source/web stamp

[aelias_OOO_until_Jul13, 2014-02-18 19:19:49]

Source/web/tests/ lgtm

[boliu, 2014-02-18 19:22:19]

The CQ bit was checked by boliu@chromium.org

[commit-bot: I haz the power, 2014-02-18 19:22:35]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/boliu@chromium.org/166093005/90001

[commit-bot: I haz the power, 2014-02-18 22:07:38]

Change committed as 167365