[Mac] Add testing code to expose an NSColor memory leak.

[Mac] Add testing code to expose an NSColor memory leak.

AutocompleteTextFieldCell calls -keyboardFocusIndicatorColor when
drawing the focus ring, which valgrind considers a leak.  While we
were testing drawing when not focussed, unit tests could not test
drawing when focussed without the window being made key, which is bad
for many reasons.

This change adds some code to allow faking the key window, then adds
tests for drawing when focussed which exposes the memory leak, then
adds a suppression for that memory leak.

http://crbug.com/21137
TEST=valgrind AutocompleteTextFieldCellTest.Display

[Scott Hess - ex-Googler, 2009-09-04 23:18:47]

John,

Unfortunately, this didn't lead to a suppression which will work for the other
leak, so I'll have to patch that separately.  But it still seems reasonable,
since this change can be leveraged to increase unit test code coverage.

[Other leak was http://codereview.chromium.org/175055
-keyboardFocusIndicatorColor call in -drawKeywordWithFrame:.]

[Scott Hess - ex-Googler, 2009-09-04 23:37:51]

On 2009/09/04 23:18:47, shess wrote:
> John,
> 
> Unfortunately, this didn't lead to a suppression which will work for the other
> leak, so I'll have to patch that separately.  But it still seems reasonable,
> since this change can be leveraged to increase unit test code coverage.
> 
> [Other leak was http://codereview.chromium.org/175055
> -keyboardFocusIndicatorColor call in -drawKeywordWithFrame:.]

Update: I just didn't understand valgrind suppressions well enough.  Now it
should cover both cases.

[John Grabowski, 2009-09-04 23:50:39]

LGTM

http://codereview.chromium.org/192031/diff/3001/2004
File chrome/browser/cocoa/cocoa_test_helper.h (right):

http://codereview.chromium.org/192031/diff/3001/2004#newcode21
Line 21: @interface CocoaTestHelperWindow : NSWindow {
Real nice how you added this in a way others can reuse.