Require a process ID when looking up RFHs by FrameTreeNode ID.

extensions/browser/extension_api_frame_id_map.cc

Index: extensions/browser/extension_api_frame_id_map.cc
diff --git a/extensions/browser/extension_api_frame_id_map.cc b/extensions/browser/extension_api_frame_id_map.cc
index bd0e19c8625cf687358a7c6ec2b8e4fce5880161..d3c43d55fcb8b4bbf36241b1d0a8f7d9cf8549c0 100644
--- a/extensions/browser/extension_api_frame_id_map.cc
+++ b/extensions/browser/extension_api_frame_id_map.cc
@@ -148,7 +148,12 @@ content::RenderFrameHost* ExtensionApiFrameIdMap::GetRenderFrameHostById(
     return web_contents->GetMainFrame();
 
   DCHECK_GE(frame_id, 1);
-  return web_contents->FindFrameByFrameTreeNodeId(frame_id);
+
+  // Unfortunately, extension APIs do not know which process to expect for a
+  // given frame ID, so we must use an unsafe API here that could return a
+  // different RenderFrameHost than the caller may have expected (e.g., one that
+  // changed after a cross-process navigation).
+  return web_contents->UnsafeFindFrameByFrameTreeNodeId(frame_id);
 }
 
 ExtensionApiFrameIdMap::FrameData ExtensionApiFrameIdMap::KeyToValue(