A DCHECK was validating a little to widely, moved it into the if that needed ...

We don't support beeing scrolled in two dimensions at a time.
This can happen when zooming on an image as identified in related bug.
So we split it in two phases.

BUG=5873
Committed: http://src.chromium.org/viewvc/chrome?view=rev&revision=10568

[MAD, 2009-02-23 22:09:01]

Not sure who to ask to review this and I saw your name in the blame list for
this file...

Feel free to ask me to ask someone else that might be more appropriate for this
review..

Thanks!

BYE
MAD

[MAD, 2009-02-24 16:34:25]

We don't know who introduced this DCHECK initially... It has been there since
the beginning of time... Can you double check if it is OK to move it? Or know
someone who would know?

Thanks!

BYE
MAD

[MAD, 2009-02-24 18:24:06]

John pointed me to Brett who pointed me to you as the author of this DCHECK line
I would like to move... Is this OK?

Thanks!

BYE
MAD

[darin (slow to review), 2009-02-24 18:56:47]

http://codereview.chromium.org/27064/diff/1/2
File chrome/renderer/render_widget.cc (right):

http://codereview.chromium.org/27064/diff/1/2#newcode559
Line 559: DCHECK((dx && !dy) || (!dx && dy));
this is not correct.  notice that scroll_delta_ will have both its x and y
elements set to non-zero.  the code is not designed to handle scrolling in both
directions.

you are probably hitting this assertion due to using auto-scroll.  i suggest
that we instead fix the code to only take the larger of the two scroll deltas. 
that way at least the behavior will be reasonable.  long term we should support
scrolling in both directions as a single operation.

[MAD, 2009-02-24 19:43:40]

OK, so how about this approach instead?

Thanks again!

BYE
MAD

[darin (slow to review), 2009-02-24 20:33:17]

http://codereview.chromium.org/27064/diff/1002/8
File webkit/glue/chrome_client_impl.cc (right):

http://codereview.chromium.org/27064/diff/1002/8#newcode413
Line 413: // RenderWidget::DidScrollRect() doesn't like to be scrolled both
ways.
it breaks abstractions to talk about RenderWidget in webkit/glue.  it would be
better to put this code in the implementation of DidScrollRect (don't forget
about TestShell!)

[MAD, 2009-02-25 14:50:20]

Like this?

[darin (slow to review), 2009-02-26 22:15:44]

LGTM

http://codereview.chromium.org/27064/diff/12/14
File chrome/renderer/render_widget.cc (right):

http://codereview.chromium.org/27064/diff/12/14#newcode553
Line 553: // We only support scrolling along one axis at a time.
this works by causing us to fall through to the slow path for scrolling, which
is fine.

http://codereview.chromium.org/27064/diff/12/13
File webkit/tools/test_shell/webwidget_host_win.cc (right):

http://codereview.chromium.org/27064/diff/12/13#newcode146
Line 146: // We only support uni-directional scroll
ditto