Adapt placement test in StatusDialogManagerTest for fractional scaling

The StatusDialogManagerTest.testBug275867() sporadically fails on
Windows because of off-by-one errors between the expected and actual
location of the shell, probably caused by rounding on fractional monitor
zooms.
To be more resilient against slight offsets in the position of the
shell, this change adds a tolerance to the position validation. It also
adds some more debug information to the failure description.

Fixes #3717

Author: HeikoKlare

tests/org.eclipse.ui.tests/Eclipse UI Tests/org/eclipse/ui/tests/statushandlers/StatusDialogManagerTest.java

@@ -774,7 +774,16 @@ public void testBug275867(){
 		wsdm.addStatusAdapter(statusAdapter, false);
 		assertNotNull(StatusDialogUtil.getStatusShell());
 		Shell shell = StatusDialogUtil.getStatusShell();
-		assertEquals("Dialog is not centered correctly",getInitialLocation(shell), shell.getLocation());
+
+		Point expected = getInitialLocation(shell);
+		Point actual = shell.getLocation();
+		int tolerance = 1;
+		assertTrue("Dialog is not centered correctly" //
+				+ " (expected location: " + expected + " ± " + tolerance //
+				+ ", actual location: " + actual //
+				+ ", dialog bounds: " + shell.getBounds() //
+				+ ", parent bounds: " + shell.getParent().getBounds() + ")",
+				Math.abs(expected.x - actual.x) <= tolerance && Math.abs(expected.y - actual.y) <= tolerance);
 	}
 
 	//error link present