Fixes issue #1253.
Adds mouse capture to SplitPanels.

Review by: jgw



git-svn-id: https://google-web-toolkit.googlecode.com/svn/trunk@1224 8db76d5a-ed1c-0410-87a9-c151d255dfc7
diff --git a/user/src/com/google/gwt/user/client/ui/SplitPanel.java b/user/src/com/google/gwt/user/client/ui/SplitPanel.java
index f96d68d..6395c00 100644
--- a/user/src/com/google/gwt/user/client/ui/SplitPanel.java
+++ b/user/src/com/google/gwt/user/client/ui/SplitPanel.java
@@ -142,18 +142,21 @@
         if (DOM.isOrHasChild(splitElem, target)) {
           startResizingFrom(DOM.eventGetClientX(event) - getAbsoluteLeft(),
               DOM.eventGetClientY(event) - getAbsoluteTop());
+          DOM.setCapture(getElement());
           DOM.eventPreventDefault(event);
         }
         break;
       }
 
       case Event.ONMOUSEUP: {
+        DOM.releaseCapture(getElement());
         stopResizing();
         break;
       }
 
       case Event.ONMOUSEMOVE: {
         if (isResizing()) {
+          assert DOM.getCaptureElement() != null;
           onSplitterResize(DOM.eventGetClientX(event) - getAbsoluteLeft(),
               DOM.eventGetClientY(event) - getAbsoluteTop());
           DOM.eventPreventDefault(event);