Allow OOPIFs to capture mouse input while mouse button is held down

content/browser/renderer_host/render_widget_host_input_event_router.cc

Index: content/browser/renderer_host/render_widget_host_input_event_router.cc
diff --git a/content/browser/renderer_host/render_widget_host_input_event_router.cc b/content/browser/renderer_host/render_widget_host_input_event_router.cc
index d30662c17a268fe3115e4e6e9208a89d0a309bec..c9e5d8daad7091d9404ca408e18c5d5df81ea20f 100644
--- a/content/browser/renderer_host/render_widget_host_input_event_router.cc
+++ b/content/browser/renderer_host/render_widget_host_input_event_router.cc
@@ -147,9 +147,23 @@ RenderWidgetHostViewBase* RenderWidgetHostInputEventRouter::FindEventTarget(
 void RenderWidgetHostInputEventRouter::RouteMouseEvent(
     RenderWidgetHostViewBase* root_view,
     blink::WebMouseEvent* event) {
+  RenderWidgetHostViewBase* target;
   gfx::Point transformed_point;
-  RenderWidgetHostViewBase* target = FindEventTarget(
-      root_view, gfx::Point(event->x, event->y), &transformed_point);
+  if (mouse_capture_target_.target &&
+      event->type != blink::WebInputEvent::MouseDown) {

[mustaq, 2016/09/13 16:57:15]

Please also check that event modifier has at least one of
{Left,Middle,Right}ButtonDown bits set, to make sure it's a real drag case.
Otherwise, dragging out-of-window & releasing would mean a hovering mouse is
still appear captured.

[kenrb, 2016/09/13 20:01:52]

Done.

+    target = mouse_capture_target_.target;
+    transformed_point = root_view->TransformPointToCoordSpaceForView(
+        gfx::Point(event->x, event->y), target);
+  } else {
+    target = FindEventTarget(root_view, gfx::Point(event->x, event->y),
+                             &transformed_point);
+  }
+
+  if (event->type == blink::WebInputEvent::MouseUp)
+    mouse_capture_target_.target = nullptr;

[mustaq, 2016/09/13 16:57:15]

Or perhaps add the check (mentioned above) here and move this |if| to before the
above |if|.

[kenrb, 2016/09/13 20:01:53]

I have fixed this according to my current understanding of correctness. Mouse
capture now requires that either a ButtonDown modifier is set, or the event is a
MouseUp (I think we still want the capturing frame to get the MouseUp).

+  else if (event->type == blink::WebInputEvent::MouseDown)
+    mouse_capture_target_.target = target;
+
   if (!target)
     return;