perf: cache CSSTokenProvider#getToken return values

org.eclipse.tm4e.ui/src/main/java/org/eclipse/tm4e/ui/themes/css/CSSTokenProvider.java

@@ -16,6 +16,7 @@
 import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
+import java.util.concurrent.ConcurrentHashMap;
 
 import org.eclipse.jdt.annotation.Nullable;
 import org.eclipse.jface.text.TextAttribute;
@@ -46,6 +47,7 @@ public List<IStyle> getStyles() {
 	}
 
 	private final Map<IStyle, @Nullable IToken> tokenMaps = new HashMap<>();
+	private final Map<String, @Nullable IToken> getTokenReturnValueCache = new ConcurrentHashMap<>();
 
 	private final CSSParser parser;
 
@@ -86,11 +88,11 @@ public IToken getToken(@Nullable final String type) {
 		if (type == null)
 			return null;
 
-		final IStyle style = parser.getBestStyle(StringUtils.splitToArray(type, '.'));
-		if (style == null)
-			return null;
-
-		return tokenMaps.get(style);
+		return getTokenReturnValueCache.computeIfAbsent(type,
+				t -> {
+					IStyle style = parser.getBestStyle(StringUtils.splitToArray(type, '.'));
+					return style == null ? null : tokenMaps.get(style);
+				});
 	}
 
 	@Nullable