[Tentaive patch for discussion] Add Purge+Suspend metrics as UMA.

content/browser/renderer_host/render_process_host_impl.cc

Index: content/browser/renderer_host/render_process_host_impl.cc
diff --git a/content/browser/renderer_host/render_process_host_impl.cc b/content/browser/renderer_host/render_process_host_impl.cc
index 2d679e3236f31b2710423d7f5d4cf2d2d85d1a73..9e3999ab4cd6226841b702867f1d48f39dbe0ba5 100644
--- a/content/browser/renderer_host/render_process_host_impl.cc
+++ b/content/browser/renderer_host/render_process_host_impl.cc
@@ -993,6 +993,7 @@ bool RenderProcessHostImpl::Init() {
 
   is_initialized_ = true;
   init_time_ = base::TimeTicks::Now();
+  last_purge_and_suspend_time_ = base::TimeTicks::FromInternalValue(0);
   return true;
 }
 
@@ -1428,6 +1429,12 @@ bool RenderProcessHostImpl::IsWorkerRefCountDisabled() {
 
 void RenderProcessHostImpl::PurgeAndSuspend() {
   Send(new ChildProcessMsg_PurgeAndSuspend());
+  last_purge_and_suspend_time_ = base::TimeTicks::Now();
+}
+
+const base::TimeTicks& RenderProcessHostImpl::GetLastPurgeAndSuspendTime()
+    const {
+  return last_purge_and_suspend_time_;
 }
 
 mojom::RouteProvider* RenderProcessHostImpl::GetRemoteRouteProvider() {