service worker: Avoid starting up for activation during shutdown

content/browser/service_worker/service_worker_process_manager.h

Index: content/browser/service_worker/service_worker_process_manager.h
diff --git a/content/browser/service_worker/service_worker_process_manager.h b/content/browser/service_worker/service_worker_process_manager.h
index 01ddae74be78507452759ef0e7c9873acdd62790..da8443f9fe6a7373a1f2ba1ebc616f87923605ea 100644
--- a/content/browser/service_worker/service_worker_process_manager.h
+++ b/content/browser/service_worker/service_worker_process_manager.h
@@ -12,6 +12,7 @@
 #include "base/callback.h"
 #include "base/gtest_prod_util.h"
 #include "base/memory/weak_ptr.h"
+#include "base/synchronization/lock.h"
 #include "content/common/service_worker/service_worker_status_code.h"
 
 class GURL;
@@ -36,9 +37,12 @@ class CONTENT_EXPORT ServiceWorkerProcessManager {
   ~ServiceWorkerProcessManager();
 
   // Synchronously prevents new processes from being allocated
-  // and drops references to RenderProcessHosts.
+  // and drops references to RenderProcessHosts. Called on the UI thread.
   void Shutdown();
 
+  // Returns true if Shutdown() has been called. May be called by any thread.
+  bool IsShutdown();
+
   // Returns a reference to a running process suitable for starting the Service
   // Worker at |script_url|. Posts |callback| to the IO thread to indicate
   // whether creation succeeded and the process ID that has a new reference.
@@ -109,9 +113,6 @@ class CONTENT_EXPORT ServiceWorkerProcessManager {
     int process_id;
   };
 
-  // Returns true if Shutdown() has been called.
-  bool IsShutdown() const { return !browser_context_; }
-
   // Maps the process ID to its reference count.
   typedef std::map<int, int> ProcessRefMap;
 
@@ -125,9 +126,16 @@ class CONTENT_EXPORT ServiceWorkerProcessManager {
   // ChildProcessHost::kInvalidUniqueID if there is none.
   int FindAvailableProcess(const GURL& pattern);
 
-  // These fields are only accessed on the UI thread.
+  // Guarded by |browser_context_lock_|.
+  // Written only on the UI thread, so the UI thread doesn't need to acquire the
+  // lock when reading. Can be read from other threads with the lock.
   BrowserContext* browser_context_;
 
+  // Protects |browser_context_|.
+  base::Lock browser_context_lock_;
+
+  // All fields below are only accessed on the UI thread.
+
   // Maps the ID of a running EmbeddedWorkerInstance to information about the
   // process it's running inside. Since the Instances themselves live on the IO
   // thread, this can be slightly out of date: