Fix TestWebKitAPI crash introduced in r202532.

WebPageProxy::forceRepaint() could trigger a call to the didForceRepaintCallback()
after the WebPageProxy had been invalidated, causing a null de-ref of m_drawingArea.
Fix by checking for error and isValid().

* UIProcess/WebPageProxy.cpp:
(WebKit::WebPageProxy::forceRepaint):

Canonical link: https://commits.webkit.org/177291@main
git-svn-id: https://svn.webkit.org/repository/webkit/trunk@202540 268f45cc-cd09-0410-ab3c-d52691b4dbfc

Source/WebKit2/ChangeLog

@@ -1,3 +1,14 @@
+2016-06-27  Simon Fraser  <simon.fraser@apple.com>
+
+        Fix TestWebKitAPI crash introduced in r202532.
+
+        WebPageProxy::forceRepaint() could trigger a call to the didForceRepaintCallback()
+        after the WebPageProxy had been invalidated, causing a null de-ref of m_drawingArea.
+        Fix by checking for error and isValid().
+
+        * UIProcess/WebPageProxy.cpp:
+        (WebKit::WebPageProxy::forceRepaint):
+
 2016-06-27  Simon Fraser  <simon.fraser@apple.com>
 
         [iOS] Make DumpRenderTree and WebKitTestRunner in the simulator use render server snapshotting

Source/WebKit2/UIProcess/WebPageProxy.cpp

@@ -2889,6 +2889,16 @@ void WebPageProxy::forceRepaint(PassRefPtr<VoidCallback> prpCallback)
     }
 
     std::function<void (CallbackBase::Error)> didForceRepaintCallback = [this, callback](CallbackBase::Error error) {
+        if (error != CallbackBase::Error::None) {
+            callback->invalidate(error);
+            return;
+        }
+
+        if (!isValid()) {
+            callback->invalidate(CallbackBase::Error::OwnerWasInvalidated);
+            return;
+        }
+
         callAfterNextPresentationUpdate([callback](CallbackBase::Error error) {
             if (error != CallbackBase::Error::None) {
                 callback->invalidate(error);