Fix the document out-of-sync due to multi threads changing the curren…

…t workingcopy buffer

org.eclipse.jdt.ls.core/src/org/eclipse/jdt/ls/core/internal/corrections/SimilarElementsRequestor.java

@@ -272,7 +272,6 @@ public static String[] getStaticImportFavorites(ICompilationUnit cu, final Strin
 		dummyCU.append("\n}\n }"); //$NON-NLS-1$
 
 		ICompilationUnit newCU= null;
-		String contents = cu.getBuffer().getContents();
 		try {
 			newCU= cu.getWorkingCopy(null);
 			newCU.getBuffer().setContents(dummyCU.toString());
@@ -304,13 +303,9 @@ public void accept(CompletionProposal proposal) {
 			requestor.setFavoriteReferences(favorites);
 
 			newCU.codeComplete(offset, requestor);
-			// if cu is working copy, we should restore the contents saved previously.
-			if (cu.isWorkingCopy()) {
-				cu.getBuffer().setContents(contents);
-			}
 			return result.toArray(new String[result.size()]);
 		} finally {
-			if (newCU != null && !cu.isWorkingCopy()) {
+			if (newCU != null) {
 				newCU.discardWorkingCopy();
 			}
 		}