Bug 318944 CSSSWTEngineImpl leaks memory
CSSSWTEngineImpl stores too many element contexts. In a memory snapshot, the HashMap size was 15559. This is most probably a leak.
bundles/org.eclipse.e4.ui.css.core/src/org/eclipse/e4/ui/css/core/impl/engine/AbstractCSSEngine.java
* 
	 * @see org.eclipse.e4.ui.core.css.engine.CSSEngine#parseStyleSheet(java.io.Reader)
	 */
	public StyleSheet parseStyleSheet(Reader reader) throws IOException {
		InputSource source = new InputSource();
		source.setCharacterStream(reader);
		return parseStyleSheet(source);
	}
	/*
	 * (non-Javadoc)
	 * 
	 * @see org.eclipse.e4.ui.core.css.engine.CSSEngine#parseStyleSheet(java.io.InputStream)
	 */
	public StyleSheet parseStyleSheet(InputStream stream) throws IOException {
		InputSource source = new InputSource();
		source.setByteStream(stream);
		return parseStyleSheet(source);
	}
	/*
	 * (non-Javadoc)
	 * 
	 * @see org.eclipse.e4.ui.core.css.engine.CSSEngine#parseStyleSheet(org.w3c.css.sac.InputSource)
	 */
	public StyleSheet parseStyleSheet(InputSource source) throws IOException {
		
		checkInputSource(source);
		CSSParser parser = makeCSSParser();
		CSSStyleSheet styleSheet = parser.parseStyleSheet(source);
		if (documentCSS instanceof ExtendedDocumentCSS) {
			documentCSS.addStyleSheet(styleSheet);