Plumb site engagement to the renderer process.

third_party/WebKit/public/platform/site_engagement.mojom

Index: third_party/WebKit/public/platform/site_engagement.mojom
diff --git a/third_party/WebKit/public/platform/site_engagement.mojom b/third_party/WebKit/public/platform/site_engagement.mojom
new file mode 100644
index 0000000000000000000000000000000000000000..2944e2b57e0a8adb9da5a95b8b4dcc17aaa339df
--- /dev/null
+++ b/third_party/WebKit/public/platform/site_engagement.mojom
@@ -0,0 +1,19 @@
+// Copyright 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+module blink.mojom;
+
+enum EngagementLevel {
+  NONE,
+  MINIMAL,
+  LOW,
+  MEDIUM,
+  HIGH,
+  MAX,
+};
+
+interface EngagementClient {
+  // The browser tells the renderer the engagement level of the current URL.
+  SetEngagementLevel(EngagementLevel level);

[nasko, 2016/11/28 19:18:08]

I would suggest adding the URL as an explicit parameter, as navigations are
inherently a racy part of the browser, so the idea of "current URL" can mismatch
between processes.
Having an explicit URL allows the receiver to verify it. The HostZoom level
works in a similar way, if you are looking for equivalent feature.

[dominickn, 2016/11/29 07:41:22]

Done.

+};