DevTools: Fix UI.Fragments for text fragment arguments
DevTools: Fix UI.Fragments for text fragment arguments

When a fragment is not wrapped in any element, it should be
treated as an element or text node and not an attribute value.

Change-Id: Ife39f9e66dcfe27931af0f7bffaddd9a09b9bfcc
Reviewed-on: https://chromium-review.googlesource.com/1083837
Commit-Queue: Joel Einbinder <bab755abe9fee48fe544272e55f73517d4e4a725@chromium.org>
Reviewed-by: Dmitry Gozman <0ca14b32cbb359a30ac562af27dd84cc2813eacb@chromium.org>
Cr-Original-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#564298}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: 87041be6fb630fb549c175d89c2fbcb674bb536f
ChromeDevTools/devtools-frontend,ChromeDevTools/devtools-frontend,ChromeDevTools/devtools-frontend,dart-archive/devtools-frontend,dart-archive/devtools-frontend,ChromeDevTools/devtools-frontend,dart-archive/devtools-frontend,ChromeDevTools/devtools-frontend,dart-archive/devtools-frontend,ChromeDevTools/devtools-frontend,dart-archive/devtools-frontend,dart-archive/devtools-frontend