DevTools: Wrap lines when editing css in styles sidebar

Bug: 778465
Change-Id: I3c4dac92b6c532058f6994ebe3cb12fc267dc8ed
Reviewed-on: https://chromium-review.googlesource.com/761257Reviewed-by: Dmitry Gozman <dgozman@chromium.org>
Commit-Queue: Joel Einbinder <einbinder@chromium.org>
Cr-Commit-Position: refs/heads/master@{#515710}

third_party/WebKit/Source/devtools/front_end/elements/stylesSectionTree.css

@@ -72,6 +72,10 @@
     padding-left: 8px;
 }
 
+.tree-outline > li.child-editing .text-prompt {
+    white-space: pre-wrap;
+}
+
 .tree-outline > li.child-editing .webkit-css-property {
     margin-left: 0;
 }