WebKit2's asynchronous plugin window positioning makes testing window geometry tricky. By
having all the trickiness in a shared base class, writing new window geometry tests will be
much easier.

Fixes <http://webkit.org/b/60776> It's hard to write tests that check plugin window geometry

Reviewed by Anders Carlsson.

* DumpRenderTree/TestNetscapePlugIn/Tests/win/WindowRegionIsSetToClipRect.cpp:
(WindowRegionIsSetToClipRect::WindowRegionIsSetToClipRect): Changed to inherit from the new
WindowGeometryTest base class. Most of the code from this class was moved to the new base
class.
(WindowRegionIsSetToClipRect::performWindowGeometryTest): Renamed from checkWindowRegion.
This is called by the base class when it is safe to check the window's geometry. Note that
the m_didCheckWindowRegion logic was removed completely; it has never been needed and was
just vestigial code from an earlier version of this test.

* DumpRenderTree/TestNetscapePlugIn/win/TestNetscapePlugin.vcproj: Added new
WindowGeometryTest class.

* DumpRenderTree/TestNetscapePlugIn/win/WindowGeometryTest.cpp: Added. Code came from
WindowRegionIsSetToClipRect.
(WindowGeometryTest::finishTest): This is the only change from WindowRegionIsSetToClipRect.
We now call the new virtual performWindowGeometryTest function instead of checkWindowRegion.
Subclasses can implement that function to perform their own tests.

* DumpRenderTree/TestNetscapePlugIn/win/WindowGeometryTest.h: Added.

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@86441 268f45cc-cd09-0410-ab3c-d52691b4dbfc