Prevent remote frame effective root scrollers

We don't support setting an OOPIF as the root scroller today so avoid
promoting it since some of the operations assume we're in a local frame.

Bug: 805427
Change-Id: I196e402e5e47ac86d364b705eab614758d0239b1
Reviewed-on: https://chromium-review.googlesource.com/895871
Commit-Queue: David Bokan <bokan@chromium.org>
Reviewed-by: Dave Tapuska <dtapuska@chromium.org>
Cr-Commit-Position: refs/heads/master@{#534104}

third_party/WebKit/Source/core/page/scrolling/RootScrollerController.cpp

@@ -179,9 +179,20 @@ bool RootScrollerController::IsValidRootScroller(const Element& element) const {
       !element.IsFrameOwnerElement())
     return false;
 
-  if (element.IsFrameOwnerElement() &&
-      !ToHTMLFrameOwnerElement(&element)->OwnedEmbeddedContentView())
-    return false;
+  if (element.IsFrameOwnerElement()) {
+    const HTMLFrameOwnerElement* frame_owner =
+        ToHTMLFrameOwnerElement(&element);
+
+    if (!frame_owner)
+      return false;
+
+    if (!frame_owner->OwnedEmbeddedContentView())
+      return false;
+
+    // TODO(bokan): Make work with OOPIF. crbug.com/642378.
+    if (!frame_owner->OwnedEmbeddedContentView()->IsLocalFrameView())
+      return false;
+  }
 
   if (!FillsViewport(element))
     return false;

third_party/WebKit/Source/core/page/scrolling/RootScrollerTest.cpp

@@ -762,12 +762,37 @@ TEST_P(RootScrollerTest, RemoteIFrame) {
   MainWebFrame()->FirstChild()->Swap(FrameTestHelpers::CreateRemote());
 
   // Set the root scroller in the local main frame to the iframe (which is
-  // remote).
+  // remote). Make sure we don't promote a remote frame to the root scroller.
   {
     Element* iframe = MainFrame()->GetDocument()->getElementById("iframe");
     NonThrowableExceptionState non_throw;
     MainFrame()->GetDocument()->setRootScroller(iframe, non_throw);
     EXPECT_EQ(iframe, MainFrame()->GetDocument()->rootScroller());
+    EXPECT_EQ(MainFrame()->GetDocument(),
+              EffectiveRootScroller(MainFrame()->GetDocument()));
+    MainFrameView()->UpdateAllLifecyclePhases();
+  }
+}
+
+// Make sure that if an effective root scroller becomes a remote frame, it's
+// demoted.
+TEST_P(RootScrollerTest, IFrameSwapToRemote) {
+  Initialize("root-scroller-iframe.html");
+  Element* iframe = MainFrame()->GetDocument()->getElementById("iframe");
+
+  {
+    NonThrowableExceptionState non_throw;
+    MainFrame()->GetDocument()->setRootScroller(iframe, non_throw);
+    ASSERT_EQ(iframe, EffectiveRootScroller(MainFrame()->GetDocument()));
+    MainFrameView()->UpdateAllLifecyclePhases();
+  }
+
+  // Swap in a remote frame. Make sure we revert back to the document.
+  {
+    MainWebFrame()->FirstChild()->Swap(FrameTestHelpers::CreateRemote());
+    MainFrameView()->UpdateAllLifecyclePhases();
+    EXPECT_EQ(MainFrame()->GetDocument(),
+              EffectiveRootScroller(MainFrame()->GetDocument()));
   }
 }