DevTools: Add labels to the timeline overview strips

Source/devtools/front_end/timeline/timelinePanel.css

Index: Source/devtools/front_end/timeline/timelinePanel.css
diff --git a/Source/devtools/front_end/timeline/timelinePanel.css b/Source/devtools/front_end/timeline/timelinePanel.css
index 975cdc465172caed9ea3f75b5bb2c038d35d8ead..6342986e0da22f7c55d12337634efd4de4964d92 100644
--- a/Source/devtools/front_end/timeline/timelinePanel.css
+++ b/Source/devtools/front_end/timeline/timelinePanel.css
@@ -254,6 +254,18 @@
     margin-top: 1px;
 }
 
+#timeline-overview-panel .overview-strip .timeline-overview-strip-placeholder {
+    position: absolute;
+    right: 0;
+    bottom: 1px;
+    color: #888;
+    padding: 0 4px;
+    font-size: 11px;
+    font-weight: bold;
+    text-transform: uppercase;
+    background-color: hsla(0, 0%, 100%, 0.6);
+}
+
 #timeline-overview-main-thread,
 #timeline-overview-framerate {
     flex-basis: 20px;
@@ -262,11 +274,11 @@
 #timeline-overview-input,
 #timeline-overview-other-threads,
 #timeline-overview-responsiveness {
-    flex-basis: 8px;
+    flex-basis: 10px;
 }
 
 #timeline-overview-network {
-    flex-basis: 39px;
+    flex-basis: 35px;
 }
 
 #timeline-overview-memory {