oom_intervention: Check OomInterventionHost binding in StartMonitoringIfNeeded()

When we observe high memory usage in renderer process, |binding_| could
be already bound when StartMonitoringIfNeeded() is called. Check if it
is already bound in StartMonitoringIfNeeded().

Bug: 817873
Change-Id: I4c75b48471a7de839fd2a159edf5f87db89c8c1d
Reviewed-on: https://chromium-review.googlesource.com/954892Reviewed-by: Kentaro Hara <haraken@chromium.org>
Commit-Queue: Kenichi Ishibashi <bashi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#541756}

chrome/browser/android/oom_intervention/oom_intervention_tab_helper.cc

@@ -247,6 +247,8 @@ void OomInterventionTabHelper::StartMonitoringIfNeeded() {
     return;
 
   if (ShouldDetectInRenderer()) {
+    if (binding_.is_bound())
+      return;
     StartDetectionInRenderer();
   } else {
     subscription_ = NearOomMonitor::GetInstance()->RegisterCallback(
@@ -277,6 +279,7 @@ void OomInterventionTabHelper::StartDetectionInRenderer() {
   DCHECK(render_process_host);
   content::BindInterface(render_process_host,
                          mojo::MakeRequest(&intervention_));
+  DCHECK(!binding_.is_bound());
   blink::mojom::OomInterventionHostPtr host;
   binding_.Bind(mojo::MakeRequest(&host));
   intervention_->StartDetection(std::move(host), trigger_intervention);