Bug 845595 - Make nsIDOMWindowUtils::selectAtPoint coordinates relative to the DWU's document. r=jimm

dom/base/nsDOMWindowUtils.cpp

@@ -3011,8 +3011,9 @@ nsDOMWindowUtils::SelectAtPoint(float aX, float aY, uint32_t aSelectBehavior,
   }
 
   // Get the target frame at the client coordinates passed to us
-  nsCOMPtr<nsIWidget> widget = GetWidget();
-  nsIntPoint pt(aX, aY);
+  nsPoint offset;
+  nsCOMPtr<nsIWidget> widget = GetWidget(&offset);
+  nsIntPoint pt = ToWidgetPoint(aX, aY, offset, GetPresContext());
   nsPoint ptInRoot =
     nsLayoutUtils::GetEventCoordinatesRelativeTo(widget, pt, rootFrame);
   nsIFrame* targetFrame = nsLayoutUtils::GetFrameForPoint(rootFrame, ptInRoot);

dom/tests/mochitest/chrome/selectAtPoint.html

@@ -164,8 +164,8 @@
 
     let rect = frame.getBoundingClientRect();
 
-    let targetPoint = { xPos: rect.left + (charDims.width / 2),
-                        yPos: rect.top + (charDims.height / 2) };
+    let targetPoint = { xPos: charDims.width / 2,
+                        yPos: charDims.height / 2 };
     setSingle(dwuFrame, targetPoint.xPos, targetPoint.yPos, Ci.nsIDOMWindowUtils.SELECT_WORDNOSPACE);
     checkSelection(frame.contentWindow.document, "SELECT_WORDNOSPACE", "ttestselection2");
     setSingle(dwuFrame, targetPoint.xPos, targetPoint.yPos, Ci.nsIDOMWindowUtils.SELECT_WORD);