Exclude files from FileSelectChooser if they can't convert to WebStrings.

content/browser/frame_host/render_frame_host_impl.cc

Index: content/browser/frame_host/render_frame_host_impl.cc
diff --git a/content/browser/frame_host/render_frame_host_impl.cc b/content/browser/frame_host/render_frame_host_impl.cc
index 0bac45b820d0a3acd252cf705c0326a96ad2a634..4656db6f4f4857df6e80c84a94e0d4e4471c278c 100644
--- a/content/browser/frame_host/render_frame_host_impl.cc
+++ b/content/browser/frame_host/render_frame_host_impl.cc
@@ -3218,6 +3218,12 @@ void RenderFrameHostImpl::FilesSelectedInChooser(
           ->GetFileSystemContext();
   // Grant the security access requested to the given files.
   for (const auto& file : files) {
+    // We shouldn't be given a FilePath that can't survive the conversion to a
+    // WebString, which we can approximate with AsUTF8Unsafe.  Blink won't be
+    // able to handle it, and we would kill the renderer when it claims to have
+    // chosen an empty file path.
+    DCHECK(!file.file_path.AsUTF8Unsafe().empty());
+
     if (permissions == FileChooserParams::Save) {
       ChildProcessSecurityPolicyImpl::GetInstance()->GrantCreateReadWriteFile(
           GetProcess()->GetID(), file.file_path);