Add flush before we find our pres context, to fix media queries tests on ringmark. (Bug 753777) r=bzbarsky

dom/base/nsGlobalWindow.cpp

@@ -3967,6 +3967,14 @@ nsGlobalWindow::MatchMedia(const nsAString& aMediaQueryList,
 
   *aResult = nsnull;
 
+  // We need this now to ensure that we have a non-null |presContext|
+  // when we ought to.
+  // This is similar to EnsureSizeUpToDate, but only flushes frames.
+  nsGlobalWindow *parent = static_cast<nsGlobalWindow*>(GetPrivateParent());
+  if (parent) {
+    parent->FlushPendingNotifications(Flush_Frames);
+  }
+
   if (!mDocShell)
     return NS_OK;
 

layout/style/test/test_media_query_list.html

@@ -280,6 +280,19 @@ function run() {
     mql.removeListener(null);
   })();
 
+  /* Bug 753777: test that things work in a freshly-created iframe */
+  (function() {
+    var iframe = document.createElement("iframe");
+    document.body.appendChild(iframe);
+
+    is(iframe.contentWindow.matchMedia("(min-width: 1px)").matches, true,
+       "(min-width: 1px) should match in newly-created iframe");
+    is(iframe.contentWindow.matchMedia("(max-width: 1px)").matches, false,
+       "(max-width: 1px) should not match in newly-created iframe");
+
+    document.body.removeChild(iframe);
+  })();
+
   /* Bug 716751: listeners lost due to GC */
   var gc_received = [];
   (function() {