MacViews: Implement SetCursor

MacViews: Implement NativeWidgetMac::SetCursor()

Tracking areas in Cocoa are a horrible mess. 10.5 semi-deprecated
NSWindow cursorRects, and introduced [NSResponder cursorUpdate:]. Both
are supported and they react with each other in strange ways.
Intercepting events for toolkit-views SetCapture seems to further
complicate things.

After numerous dead-ends, this CL implements SetCursor() by overriding
cursorUpdate: on NativeWidgetMac's NSWindow override. This works because
cursorUpdate: messages are forwarded along the responder chain (starting
from varied and somewhat unpredictable starting points), and usually end
up at the NSWindow.

Rather than adding more NSTrackingArea cruft, the one in
BridgedContentView is updated to handle cursor updates. This ensures the
cursor is reset to "normal" whenever it leaves the content area.

Installing a global event monitor also resets the mouse cursor to an
arrow. I tried tracing this with NSObjCMessageLoggingEnabled, but the
reset isn't done with Objective-C. To fix, "remind" AppKit what the
cursor should be after setting capture.

See code comments for all the other traps.

Testing tracking rectangles with simulated events is pretty much a lost
cause, but NativeWidgetMacTest.SetCursor() is added which gets some
coverage by sending an event directly to [NSWindow cursorUpdate:], and
using the ui::test::EventGenerator to forward events to toolkit-views to
actually request new cursors to set.

BUG=454698
Committed: https://crrev.com/715cb510d3fe596bf604c2e48741fbc08d1e9aee
Cr-Commit-Position: refs/heads/master@{#314660}

[tapted, 2015-02-03 07:50:36]

tapted@chromium.org changed reviewers:
+ andresantoso@chromium.org, rsesek@chromium.org

[tapted, 2015-02-03 07:58:46]

Hi Andre and Robert.. adding you both as reviewers since this CL turned out to
be about a billion times more complicated than I thought it would be :/

RenderWidgetViewMac uses cursorRects, but it seems pretty buggy. E.g. click a
link and drag over the link text and the cursor flickers. Managing these cursor
rects is complicated, and even updating the cursorRect while the cursor is
"inside" the view, seems like a dead end. The approach here avoids simply
mashing [NSCursor set] on every mouse event, which seems to be what content
does.

So, this seems to be a straightforward solution without adding too much more
complexity. It's just that initial sometimes-flicker on mousedown that I'm
concerned about (most of the time it doesn't even happen), but I have a TODO
that I think will get a nice outcome there too.

[Andre, 2015-02-04 02:05:56]

LGTM

https://codereview.chromium.org/891003004/diff/100001/ui/views/cocoa/views_ns...
File ui/views/cocoa/views_nswindow_delegate.h (right):

https://codereview.chromium.org/891003004/diff/100001/ui/views/cocoa/views_ns...
ui/views/cocoa/views_nswindow_delegate.h:31: @property(assign, nonatomic)
NSCursor* cursor;
Should be documented as retain not assign, even though you are not using a
synthesized setter.

[tapted, 2015-02-04 08:41:39]

New patchsets have been uploaded after l-g-t-m from andresantoso@chromium.org

[tapted, 2015-02-04 08:49:28]

Robert - do you see any red flags in this approach?

https://codereview.chromium.org/891003004/diff/100001/ui/views/cocoa/views_ns...
File ui/views/cocoa/views_nswindow_delegate.h (right):

https://codereview.chromium.org/891003004/diff/100001/ui/views/cocoa/views_ns...
ui/views/cocoa/views_nswindow_delegate.h:31: @property(assign, nonatomic)
NSCursor* cursor;
On 2015/02/04 02:05:55, Andre wrote:
> Should be documented as retain not assign, even though you are not using a
> synthesized setter.
> 

Done.

[Robert Sesek, 2015-02-04 15:58:50]

LGTM, sorry I didn't get to this yesterday.

[tapted, 2015-02-04 22:00:07]

Thanks for taking a look!

[tapted, 2015-02-04 22:00:15]

The CQ bit was checked by tapted@chromium.org

[commit-bot: I haz the power, 2015-02-04 22:00:46]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/891003004/140001

[commit-bot: I haz the power, 2015-02-04 22:25:24]

Committed patchset #8 (id:140001)

[commit-bot: I haz the power, 2015-02-04 22:28:07]

Patchset 8 (id:??) landed as
https://crrev.com/715cb510d3fe596bf604c2e48741fbc08d1e9aee
Cr-Commit-Position: refs/heads/master@{#314660}