UMA for measuring how often 2 or more tabs script the same background contents.

chrome/browser/background/background_contents.cc

Index: chrome/browser/background/background_contents.cc
diff --git a/chrome/browser/background/background_contents.cc b/chrome/browser/background/background_contents.cc
index a419a5471ad2ea05fa84e208c68419d68a793feb..5eb57800c75ed5c78653b7c40d9399688f848343 100644
--- a/chrome/browser/background/background_contents.cc
+++ b/chrome/browser/background/background_contents.cc
@@ -6,6 +6,9 @@
 
 #include <utility>
 
+#include "base/bind.h"
+#include "base/callback.h"
+#include "base/metrics/histogram_macros.h"
 #include "base/profiler/scoped_tracker.h"
 #include "chrome/browser/background/background_contents_service.h"
 #include "chrome/browser/chrome_notification_types.h"
@@ -26,6 +29,7 @@
 #include "extensions/browser/deferred_start_render_host_observer.h"
 #include "extensions/browser/extension_host_delegate.h"
 #include "extensions/browser/extension_host_queue.h"
+#include "extensions/browser/extension_registry.h"
 #include "extensions/browser/extensions_browser_client.h"
 #include "extensions/browser/view_type_utils.h"
 #include "ui/gfx/geometry/rect.h"
@@ -44,7 +48,8 @@ BackgroundContents::BackgroundContents(
     content::SessionStorageNamespace* session_storage_namespace)
     : delegate_(delegate),
       extension_host_delegate_(extensions::ExtensionsBrowserClient::Get()
-                                   ->CreateExtensionHostDelegate()) {
+                                   ->CreateExtensionHostDelegate()),
+      weak_factory_(this) {
   profile_ = Profile::FromBrowserContext(
       site_instance->GetBrowserContext());
 
@@ -66,6 +71,7 @@ BackgroundContents::BackgroundContents(
   } else {
     web_contents_.reset(WebContents::Create(create_params));
   }
+  TrackPreviousOpener();
   extensions::SetViewType(
       web_contents_.get(), extensions::VIEW_TYPE_BACKGROUND_CONTENTS);
   web_contents_->SetDelegate(this);
@@ -92,9 +98,7 @@ BackgroundContents::BackgroundContents(
 
 // Exposed to allow creating mocks.
 BackgroundContents::BackgroundContents()
-    : delegate_(NULL),
-      profile_(NULL) {
-}
+    : delegate_(NULL), profile_(NULL), weak_factory_(this) {}
 
 BackgroundContents::~BackgroundContents() {
   if (!web_contents_.get())   // Will be null for unit tests.
@@ -230,3 +234,73 @@ void BackgroundContents::RemoveDeferredStartRenderHostObserver(
     extensions::DeferredStartRenderHostObserver* observer) {
   deferred_start_render_host_observer_list_.RemoveObserver(observer);
 }
+
+namespace {
+
+class OpenerDestroyedObserver : public content::WebContentsObserver {
+ public:
+  OpenerDestroyedObserver(content::RenderFrameHost* opener,
+                          base::OnceClosure callback)
+      : WebContentsObserver(WebContents::FromRenderFrameHost(opener)),
+        opener_(opener),
+        callback_(std::move(callback)) {
+    DCHECK(!callback_.is_null());
+  }
+
+  // WebContentsObserver override:
+  void RenderFrameDeleted(content::RenderFrameHost* deleted_frame) override {
+    if (deleted_frame == opener_) {
+      std::move(callback_).Run();
+      delete this;
+    }
+  }
+
+ private:
+  content::RenderFrameHost* opener_;
+  base::OnceClosure callback_;
+  DISALLOW_COPY_AND_ASSIGN(OpenerDestroyedObserver);
+};
+
+}  // namespace
+
+void BackgroundContents::TrackPreviousOpener() {
+  // Do we already have a still-alive previous opener that is a hosted app?
+  if (previous_opener_)
+    return;
+
+  if (!IsCurrentOpenerHostedApp())
+    return;
+
+  previous_opener_ = web_contents()->GetOpener();
+  DCHECK(previous_opener_);
+  new OpenerDestroyedObserver(
+      previous_opener_,
+      base::Bind(&BackgroundContents::OnPreviousOpenerDestroyed,
+                 weak_factory_.GetWeakPtr()));
+}
+
+void BackgroundContents::OnPreviousOpenerDestroyed() {
+  previous_opener_ = nullptr;
+}
+
+bool BackgroundContents::IsCurrentOpenerHostedApp() {
+  content::RenderFrameHost* current_opener = web_contents()->GetOpener();
+  if (!current_opener)
+    return false;
+
+  const extensions::Extension* opener_extension =
+      extensions::ExtensionRegistry::Get(web_contents()->GetBrowserContext())
+          ->enabled_extensions()
+          .GetExtensionOrAppByURL(current_opener->GetLastCommittedURL());
+  return opener_extension && opener_extension->is_hosted_app();
+}
+
+void BackgroundContents::DidChangeOpener() {
+  if (previous_opener_ && IsCurrentOpenerHostedApp() &&
+      (web_contents()->GetOpener() != previous_opener_)) {
+    UMA_HISTOGRAM_BOOLEAN(
+        "Extensions.HostedAppOpenedBackgroundContentsFromTwoOpeners", true);
+  }
+
+  TrackPreviousOpener();
+}