[DevTools] Migrate RequestHeadersView to TreeOutlineInShadow.

third_party/WebKit/Source/devtools/front_end/ui/treeoutline.css

Index: third_party/WebKit/Source/devtools/front_end/ui/treeoutline.css
diff --git a/third_party/WebKit/Source/devtools/front_end/ui/treeoutline.css b/third_party/WebKit/Source/devtools/front_end/ui/treeoutline.css
index e418cfb9282d411b439322e319e953defe7f93db..42a899db6a39d233ccb4a19f27ca6fb60029027f 100644
--- a/third_party/WebKit/Source/devtools/front_end/ui/treeoutline.css
+++ b/third_party/WebKit/Source/devtools/front_end/ui/treeoutline.css
@@ -125,3 +125,20 @@ ol.tree-outline:focus li.selected * {
 .tree-outline ol.children.expanded {
     display: block;
 }
+
+.tree-outline.tree-outline-dense li {
+    margin-top: 1px;
+    min-height: 12px;
+}
+
+.tree-outline.tree-outline-dense li.parent {
+    margin-top: 0;
+}
+
+.tree-outline.tree-outline-dense li.parent::before {
+    top: 0;
+}
+
+.tree-outline.tree-outline-dense ol {
+    padding-left: 10px;
+}