Fix issue #6724 - clearOpacity doesn't clear the "filter" property in IE8.

Review at: http://gwt-code-reviews.appspot.com/1615805
Patch by: stephenh

Review by: jlabanca@google.com

git-svn-id: https://google-web-toolkit.googlecode.com/svn/trunk@10941 8db76d5a-ed1c-0410-87a9-c151d255dfc7
diff --git a/user/src/com/google/gwt/dom/client/DOMImplIE8.java b/user/src/com/google/gwt/dom/client/DOMImplIE8.java
index 294aa49..1772c44 100644
--- a/user/src/com/google/gwt/dom/client/DOMImplIE8.java
+++ b/user/src/com/google/gwt/dom/client/DOMImplIE8.java
@@ -44,6 +44,15 @@
   }-*/;
 
   @Override
+  public void cssClearOpacity(Style style) {
+    if (isIE8()) {
+      cssClearOpacityImpl(style);
+    } else {
+      super.cssClearOpacity(style);
+    }
+  }
+
+  @Override
   public void cssSetOpacity(Style style, double value) {
     if (isIE8()) {
       cssSetOpacityImpl(style, value);
@@ -82,6 +91,10 @@
     super.setScrollLeft(elem, left);
   }
 
+  private native void cssClearOpacityImpl(Style style) /*-{
+    style.filter = '';
+  }-*/;
+
   private native void cssSetOpacityImpl(Style style, double value) /*-{
     style.filter = 'alpha(opacity=' + (value * 100) + ')';
   }-*/;