Bug 1585320 - Always show request blocking top bar r=Honza

Differential Revision: https://phabricator.services.mozilla.com/D48992

--HG--
extra : moz-landing-system : lando

devtools/client/netmonitor/src/assets/styles/RequestBlockingPanel.css

@@ -2,6 +2,12 @@
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
+.network-monitor .request-blocking-panel {
+  overflow: hidden;
+  position: relative;
+  height: 100%;
+}
+
 /* The "Enable Blocking Requests" bar */
 .network-monitor .request-blocking-enable-bar {
   background: var(--theme-tab-toolbar-background);
@@ -37,11 +43,22 @@
   cursor: default;
 }
 
+.request-blocking-contents {
+  position: absolute;
+  bottom: 0;
+  top: 26px;
+  left: 0;
+  right: 0;
+  overflow-y: auto;
+}
+
+
 /* Blocked request list */
 .network-monitor .request-blocking-list {
   margin: 0;
   padding: 0;
   border-bottom: 1px solid var(--theme-splitter-color);
+  width: 100%;
 }
 
 .network-monitor .request-blocking-list li {

devtools/client/netmonitor/src/components/request-blocking/RequestBlockingPanel.js

@@ -229,8 +229,11 @@ class RequestBlockingPanel extends Component {
     return div(
       { className: "request-blocking-panel" },
       this.renderEnableBar(),
-      this.renderBlockedList(),
-      this.renderAddForm()
+      div(
+        { className: "request-blocking-contents" },
+        this.renderBlockedList(),
+        this.renderAddForm()
+      )
     );
   }
 }