Bug 42313 - unable to scroll over iframes with mousewheel. We now

correctly bubble up the scroll to the parent document if the iframe is
unable to scroll (either because it isn't scrollable, or because we're
already at the top/bottom of it).  r=saari, sr=hyatt.

content/events/src/nsEventStateManager.cpp

@@ -1359,19 +1359,37 @@ nsEventStateManager::DoWheelScroll(nsIPresContext* aPresContext,
     sv = GetNearestScrollingView(focusView);
   }
 
+  PRBool passToParent = PR_FALSE;
+
   if (sv) {
     if (targetContent)
       targetContent->HandleDOMEvent(aPresContext, &mouseOutEvent, nsnull,
                                     NS_EVENT_FLAG_INIT, &mouseoutStatus);
 
+    // Check the scroll position before and after calling ScrollBy[Page|Line]s.
+    // This allows us to detect whether the view is not scrollable
+    // (for whatever reason) and bubble up the scroll to the parent document.
+
+    nscoord xPos, yPos;
+    sv->GetScrollPosition(xPos, yPos);
+
     if (scrollPage)
       sv->ScrollByPages((numLines > 0) ? 1 : -1);
     else
       sv->ScrollByLines(0, numLines);
 
+    nscoord newXPos, newYPos;
+    sv->GetScrollPosition(newXPos, newYPos);
+
+    if (newYPos != yPos) {
       if (focusView)
         ForceViewUpdate(focusView);
-  } else {
+    } else
+      passToParent = PR_TRUE;
+  } else
+    passToParent = PR_TRUE;
+
+  if (passToParent) {
     nsresult rv;
     nsIFrame* newFrame = nsnull;
     nsCOMPtr<nsIPresContext> newPresContext;
@@ -1404,6 +1422,7 @@ nsEventStateManager::GetParentScrollingView(nsMouseScrollEvent *aEvent,
   nsCOMPtr<nsIDocShellTreeItem> treeItem = do_QueryInterface(shell);
   if (!treeItem) return NS_ERROR_FAILURE;
 
+  /* get our docshell's parent */
   nsCOMPtr<nsIDocShellTreeItem> parent;
   treeItem->GetParent(getter_AddRefs(parent));
   if (!parent) return NS_ERROR_FAILURE;
@@ -1411,35 +1430,37 @@ nsEventStateManager::GetParentScrollingView(nsMouseScrollEvent *aEvent,
   nsCOMPtr<nsIDocShell> pDocShell = do_QueryInterface(parent);
   if (!pDocShell) return NS_ERROR_FAILURE;
 
-  nsCOMPtr<nsIPresShell> presShell;
-  pDocShell->GetPresShell(getter_AddRefs(presShell));
-  if (!presShell) return NS_ERROR_FAILURE;
+  nsCOMPtr<nsIPresShell> pPresShell;
+  pDocShell->GetPresShell(getter_AddRefs(pPresShell));
+  if (!pPresShell) return NS_ERROR_FAILURE;
 
-  nsIFrame* rootFrame = nsnull;
-  presShell->GetRootFrame(&rootFrame);   
-  if (!rootFrame) return NS_ERROR_FAILURE;
+  nsCOMPtr<nsIDocument> parentDoc;
+  pPresShell->GetDocument(getter_AddRefs(parentDoc));
 
-  presShell->GetPresContext(&presCtxOuter); //addrefs
+  nsCOMPtr<nsIContent> rootContent;
+  parentDoc->GetRootContent(getter_AddRefs(rootContent));
 
-  nsPoint eventPoint;
-  rootFrame->GetOrigin(eventPoint);
-  eventPoint += aEvent->point;
+  nsCOMPtr<nsIDocShell> ourDS = do_QueryInterface(shell);
 
-  nsresult rv;
-  rv = rootFrame->GetFrameForPoint(presCtxOuter, eventPoint,
-                                   NS_FRAME_PAINT_LAYER_FOREGROUND,
-                                   &targetOuterFrame);
-  if (rv != NS_OK) {
-    rv = rootFrame->GetFrameForPoint(presCtxOuter, eventPoint,
-                                     NS_FRAME_PAINT_LAYER_FLOATERS,
-                                     &targetOuterFrame);
-    if (rv != NS_OK) {
-      rv = rootFrame->GetFrameForPoint(presCtxOuter, eventPoint,
-                                       NS_FRAME_PAINT_LAYER_BACKGROUND,
-                                       &targetOuterFrame);
-      if (rv != NS_OK) return NS_ERROR_FAILURE;
-    }
-  }
+  /* now find the content node in our parent docshell's document that corresponds
+     to our docshell */
+  nsCOMPtr<nsIContent> frameContent = getter_AddRefs(FindContentForDocShell(pPresShell, 
+                                                                            rootContent,
+                                                                            ourDS));
+  if (!frameContent) return NS_ERROR_FAILURE;
+
+  /*
+    get this content node's frame, and use it as the new event target,
+    so the event can be processed in the parent docshell.
+    Note that we don't actually need to translate the event coordinates
+    because they are not used by DoWheelScroll().
+  */
+  nsIFrame* frameFrame = nsnull;
+  pPresShell->GetPrimaryFrameFor(frameContent, &frameFrame);
+  if (!frameFrame) return NS_ERROR_FAILURE;
+
+  pPresShell->GetPresContext(&presCtxOuter); //addrefs
+  targetOuterFrame = frameFrame;
 
   return NS_OK;
 }