[Mac] Fix weird layout issues when dragging a tab from a large screen to a sm...

[Mac] Fix weird layout issues when dragging a tab from a large screen to a small one.

BUG=http://crbug.com/27652
TEST=With two monitors of different vertical sizes connected, make a chrome window on the larger monitor, as tall as the monitor.  Drag it over to the smaller monitor and drop it.  The window should not re-layout weirdly during the drag and should continue to have a tab strip after the drop.

Committed: http://src.chromium.org/viewvc/chrome?view=rev&revision=31967

[pink (ping after 24hrs), 2009-11-13 21:02:36]

we're discussing a better idea on irc. this wasn't intended to be LGTM'd.

[rohitrao (ping after 24h), 2009-11-13 21:24:35]

Ok, this is better now, but be warned that I plan to sneak the awesome
alphaValue hack back into the code somewhere.

[pink (ping after 24hrs), 2009-11-13 21:33:52]

http://codereview.chromium.org/385106/diff/4/2001
File chrome/browser/cocoa/chrome_browser_window.mm (right):

http://codereview.chromium.org/385106/diff/4/2001#newcode335
Line 335: if ([[self delegate] overlayWindow])
you should ensure that the delegate responds to the selector before calling it.

It would also probably be better if this wasn't using overlayWindow directly,
because again this window shouldn't know anything about that impl detail. It
shoudl just ask its delegate "canConstrainFrameRect?" or something and return
frame based on that response.

[pink (ping after 24hrs), 2009-11-13 21:35:11]

or better still, just pass the constrainFrameRect:inScreen: to the delegate and
have it return the appropriate rect. That way the delegate can do wahtever it
wants in the future.

[pink (ping after 24hrs), 2009-11-13 22:09:57]

LGTM

http://codereview.chromium.org/385106/diff/6/7
File chrome/browser/cocoa/chrome_browser_window.mm (right):

http://codereview.chromium.org/385106/diff/6/7#newcode332
Line 332: - (NSRect)constrainFrameRect:(NSRect)frame toScreen:(NSScreen*)screen
{
add a comment on when and why this gets called.