Introduce enableLegacyPatching flag for CSS patching

As part of the dark mode migration we are adding
`enableLegacyPatching:true` to all call sites of `appendStyle` (and
related methods). If a user passes `false` for that flag, no CSS colour
patching will occur.

This CL is therefore a no-op from a user's perspective as we pass `true`
on every call to maintain existing behaviour, but once we start
migrating we will turn the option to `false`. Long term, once all code
is migrated and the old patching is removed, we will remove this flag
entirely once again.

Bug: 1122511
Change-Id: I76b818e83b7d5ee0175e1548759373f53481e0ab
No-Presubmit: True
Reviewed-on: https://chromium-review.googlesource.com/c/devtools/devtools-frontend/+/2516345
Commit-Queue: Jack Franklin <[email protected]>
Reviewed-by: Tim van der Lippe <[email protected]>
diff --git a/front_end/console/ConsoleSidebar.js b/front_end/console/ConsoleSidebar.js
index 028249c..09e79da 100644
--- a/front_end/console/ConsoleSidebar.js
+++ b/front_end/console/ConsoleSidebar.js
@@ -17,7 +17,7 @@
     this.setMinimumSize(125, 0);
 
     this._tree = new UI.TreeOutline.TreeOutlineInShadow();
-    this._tree.registerRequiredCSS('console/consoleSidebar.css');
+    this._tree.registerRequiredCSS('console/consoleSidebar.css', {enableLegacyPatching: true});
     this._tree.addEventListener(UI.TreeOutline.Events.ElementSelected, this._selectionChanged.bind(this));
     this.contentElement.appendChild(this._tree.element);
     /** @type {?UI.TreeOutline.TreeElement} */