Allow middle-click scrolling to work for PDFs and print preview

This tells the plugin not to handle middle-click events so that they are
properly handled by the container page and allows middle-click scrolling
to work.

BUG=463399

Review URL: https://codereview.chromium.org/976123002

Cr-Commit-Position: refs/heads/master@{#319366}

1 files changed, 6 insertions, 2 deletions

diff --git a/pdf/out_of_process_instance.cc b/pdf/out_of_process_instance.cc
index ee4cd9f..f40582d 100644
--- a/pdf/out_of_process_instance.cc
+++ b/pdf/out_of_process_instance.cc
@@ -550,8 +550,12 @@ bool OutOfProcessInstance::HandleInputEvent(
   if (engine_->HandleEvent(offset_event))
     return true;
 
-  // TODO(raymes): Implement this scroll behavior in JS:
-  // When click+dragging, scroll the document correctly.
+  // Middle click is used for scrolling and is handled by the container page.
+  pp::MouseInputEvent mouse_event(event_device_res);
+  if (!mouse_event.is_null() &&
+      mouse_event.GetButton() == PP_INPUTEVENT_MOUSEBUTTON_MIDDLE) {
+    return false;
+  }
 
   // Return true for unhandled clicks so the plugin takes focus.
   return (event.GetType() == PP_INPUTEVENT_TYPE_MOUSEDOWN);