DevTools: Add contain strict to metrics sidebar

This should make the color picker much faster

Bug: none
Change-Id: I487616d71e430cb6c8374473bc1d84d7810f10cf
Reviewed-on: https://chromium-review.googlesource.com/807545
Commit-Queue: Joel Einbinder <einbinder@chromium.org>
Reviewed-by: Pavel Feldman <pfeldman@chromium.org>
Cr-Commit-Position: refs/heads/master@{#521594}

third_party/WebKit/Source/devtools/front_end/elements/metricsSidebarPane.css

@@ -9,13 +9,19 @@
     font-size: 10px;
     text-align: center;
     white-space: nowrap;
-    min-height: 190px;
+    min-height: var(--metrics-height);
     display: flex;
     flex-direction: column;
     -webkit-align-items: center;
     -webkit-justify-content: center;
 }
 
+:host {
+    --metrics-height: 190px;
+    height: var(--metrics-height);
+    contain: strict;
+}
+
 :host-context(.-theme-with-dark-background) .metrics {
     color: #222;
 }