[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..d72ef14963b6777e7862d03e0544f5ed2008d56c 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),
@@ -995,6 +996,9 @@ void RenderFrameHostImpl::RenderProcessGone(SiteInstanceImpl* site_instance) {
   // Any future UpdateState or UpdateTitle messages from this or a recreated
   // process should be ignored until the next commit.
   set_nav_entry_id(0);
+
+  if (is_audible_)
+    GetProcess()->OnAudioStreamRemoved();
 }
 
 void RenderFrameHostImpl::ReportContentSecurityPolicyViolation(
@@ -1182,6 +1186,20 @@ void RenderFrameHostImpl::Init() {
   }
 }
 
+bool RenderFrameHostImpl::IsAudible() {
+  return is_audible_;
+}
+
+void RenderFrameHostImpl::OnAudioStateChanged(bool is_audible) {
+  if (is_audible != is_audible_) {

[DaleCurtis, 2017/06/22 00:35:54]

early return is preferred.

[lpy, 2017/06/22 02:28:52]

Done.

+    if (is_audible)
+      GetProcess()->OnAudioStreamAdded();
+    else
+      GetProcess()->OnAudioStreamRemoved();
+  }
+  is_audible_ = is_audible;
+}
+
 void RenderFrameHostImpl::OnDidAddMessageToConsole(
     int32_t level,
     const base::string16& message,