DevTools: Grey out outside parts of selection window on timeline overview.

third_party/WebKit/Source/devtools/front_end/ui_lazy/timelineGrid.css

Index: third_party/WebKit/Source/devtools/front_end/ui_lazy/timelineGrid.css
diff --git a/third_party/WebKit/Source/devtools/front_end/ui_lazy/timelineGrid.css b/third_party/WebKit/Source/devtools/front_end/ui_lazy/timelineGrid.css
index 68d0f183ce6c7e0198d6af40b5c63a83e7de782c..3d952f41ec8d45ad10c99b6e635a50973f991d99 100644
--- a/third_party/WebKit/Source/devtools/front_end/ui_lazy/timelineGrid.css
+++ b/third_party/WebKit/Source/devtools/front_end/ui_lazy/timelineGrid.css
@@ -65,3 +65,20 @@
     height: 20px;
     pointer-events: none;
 }
+
+.timeline-curtain-left, .timeline-curtain-right {
+    background-color: hsla(0, 0%, 80%, 0.3);
+    position: absolute;
+    top: 0;
+    height: 100%;
+    z-index: 300;
+    pointer-events: none;
+}
+
+.timeline-curtain-left {
+    left: 0;
+}
+
+.timeline-curtain-right {
+    right: 0;
+}