[AudioStreamMonitor] Adds API to collect frame-level audibility.

content/browser/frame_host/render_frame_host_impl.cc

Index: content/browser/frame_host/render_frame_host_impl.cc
diff --git a/content/browser/frame_host/render_frame_host_impl.cc b/content/browser/frame_host/render_frame_host_impl.cc
index 3754bebcc1199260ee1c9cc6f5b904c7936652a3..2f6aff6052158df84b089f50f41c9f9b45e51241 100644
--- a/content/browser/frame_host/render_frame_host_impl.cc
+++ b/content/browser/frame_host/render_frame_host_impl.cc
@@ -437,6 +437,7 @@ RenderFrameHostImpl::RenderFrameHostImpl(SiteInstance* site_instance,
       pending_web_ui_type_(WebUI::kNoWebUI),
       should_reuse_web_ui_(false),
       has_selection_(false),
+      is_audible_(false),
       last_navigation_previews_state_(PREVIEWS_UNSPECIFIED),
       frame_host_interface_broker_binding_(this),
       frame_host_associated_binding_(this),
@@ -3566,6 +3567,14 @@ bool RenderFrameHostImpl::HasSelection() {
   return has_selection_;
 }
 
+bool RenderFrameHostImpl::IsAudible() {
+  return is_audible_;
+}
+
+void RenderFrameHostImpl::OnAudioStateChanged(bool is_audible) {
+  is_audible_ = is_audible;
+}
+
 void RenderFrameHostImpl::GetInterfaceProvider(
     service_manager::mojom::InterfaceProviderRequest interfaces) {
   service_manager::Identity child_identity = GetProcess()->GetChildIdentity();