Devtools: Provide affordance during network recording using a pulsing anim

Source/devtools/front_end/ui/toolbar.css

Index: Source/devtools/front_end/ui/toolbar.css
diff --git a/Source/devtools/front_end/ui/toolbar.css b/Source/devtools/front_end/ui/toolbar.css
index eb2ff6926da4dcf7b912b8b7907cb44a9a055ee5..68579fbb0f79c0b4888ae3c7b56085715f34fdb5 100644
--- a/Source/devtools/front_end/ui/toolbar.css
+++ b/Source/devtools/front_end/ui/toolbar.css
@@ -323,6 +323,15 @@ button.record-toolbar-item.toggled-on .glyph {
     background-color: rgb(216, 0, 0) !important;
 }
 
+:host-context(.network) button.record-toolbar-item.toggled-on .glyph {
+    animation: pulse-effect 2.5s infinite alternate ease-in-out;
+}
+
+@keyframes pulse-effect {
+    from { transform: scale(0.8); }
+    to { transform: scale(1.1); }
+}
+
 .camera-toolbar-item .glyph {
     -webkit-mask-position: -96px -24px;
 }