DevTools: Don't have hover state for non-highlightable nodes

We don't highlight dom nodes when they are part of an object preview,
so it was misleading to have a blue hover effect on them.

Bug: none
Change-Id: I4254032016b749208f27654f7ddefdecf6937bd6
Reviewed-on: https://chromium-review.googlesource.com/740673Reviewed-by: Erik Luo <luoe@chromium.org>
Reviewed-by: Pavel Feldman <pfeldman@chromium.org>
Commit-Queue: Joel Einbinder <einbinder@chromium.org>
Cr-Commit-Position: refs/heads/master@{#512631}

third_party/WebKit/Source/devtools/front_end/object_ui/objectValue.css

@@ -19,7 +19,7 @@
     display: flex !important;
 }
 
-.object-value-node:hover {
+.value.object-value-node:hover {
     background-color: rgba(56, 121, 217, 0.1);
 }