Wait on quick diff initialize before editing CU in test

Tracings of recent SaveParticipantTest fail show the quick diff initialize job,
accessing GapTextStore in parallel to the tests. This change joins this
initialize job, prior to editing CUs from the tests - to avoid potential race conditions.

See: #79

Author: trancexpress

org.eclipse.jdt.ui.tests/ui/org/eclipse/jdt/ui/tests/quickfix/SaveParticipantTest.java

@@ -35,6 +35,8 @@
 
 import org.eclipse.jface.text.CopyOnWriteTextStore;
 
+import org.eclipse.ui.internal.texteditor.quickdiff.DocumentLineDiffer;
+
 import org.eclipse.jdt.core.IClasspathEntry;
 import org.eclipse.jdt.core.ICompilationUnit;
 import org.eclipse.jdt.core.IJavaProject;
@@ -105,6 +107,7 @@ public void tearDown() throws Exception {
 	private static void editCUInEditor(ICompilationUnit cu, String newContent) throws Exception {
 		JavaEditor editor= (JavaEditor) EditorUtility.openInEditor(cu);
 		Job.getJobManager().join(ReconcilerJobFamilies.FAMILY_RECONCILER, null);
+		Job.getJobManager().join(DocumentLineDiffer.QUICKDIFF_INITIALIZE_FAMILY, null);
 		TestUtils.cancelDecorationJob();
 
 		cu.getBuffer().setContents(newContent);