Trace background/visibility events

Trace the following events:
 * CompositorImplAndroid::SetVisility
 * RenderWidgetHost::WasHidden
 * RenderWidgetHost::WasShown
 * RenderProcessHostImpl::SetBackgrounded

These events give greater context to content behavior with respect
to visibility changes.

BUG=466213

Review URL: https://codereview.chromium.org/1032703002

Cr-Commit-Position: refs/heads/master@{#322306}

content/browser/renderer_host/compositor_impl_android.cc

@@ -438,6 +438,7 @@ void CompositorImpl::CreateLayerTreeHost() {
 }
 
 void CompositorImpl::SetVisible(bool visible) {
+  TRACE_EVENT1("cc", "CompositorImpl::SetVisible", "visible", visible);
   if (!visible) {
     DCHECK(host_);
     // Look for any layers that were attached to the root for readback

content/browser/renderer_host/render_process_host_impl.cc

@@ -2223,6 +2223,8 @@ void RenderProcessHostImpl::OnDumpHandlesDone() {
 }
 
 void RenderProcessHostImpl::SetBackgrounded(bool backgrounded) {
+  TRACE_EVENT1("renderer_host", "RenderProcessHostImpl::SetBackgrounded",
+               "backgrounded", backgrounded);
   // Note: we always set the backgrounded_ value.  If the process is NULL
   // (and hence hasn't been created yet), we will set the process priority
   // later when we create the process.

content/browser/renderer_host/render_widget_host_impl.cc

@@ -511,6 +511,7 @@ void RenderWidgetHostImpl::WasHidden() {
   if (is_hidden_)
     return;
 
+  TRACE_EVENT0("renderer_host", "RenderWidgetHostImpl::WasHidden");
   is_hidden_ = true;
 
   // Don't bother reporting hung state when we aren't active.
@@ -533,6 +534,8 @@ void RenderWidgetHostImpl::WasHidden() {
 void RenderWidgetHostImpl::WasShown(const ui::LatencyInfo& latency_info) {
   if (!is_hidden_)
     return;
+
+  TRACE_EVENT0("renderer_host", "RenderWidgetHostImpl::WasShown");
   is_hidden_ = false;
 
   SendScreenRects();