Fix race condition in content_shell which could lead to an assert on shutdown with PlzNavigate.

content/shell/browser/shell_browser_context.cc

Index: content/shell/browser/shell_browser_context.cc
diff --git a/content/shell/browser/shell_browser_context.cc b/content/shell/browser/shell_browser_context.cc
index c16359e93e3f7a8052d6f7d2c5316792dfdcee66..90f18e9ac8b96fc95361ad4275c992dc92bf5404 100644
--- a/content/shell/browser/shell_browser_context.cc
+++ b/content/shell/browser/shell_browser_context.cc
@@ -67,11 +67,15 @@ ShellBrowserContext::ShellBrowserContext(bool off_the_record,
 ShellBrowserContext::~ShellBrowserContext() {
   BrowserContextDependencyManager::GetInstance()->
       DestroyBrowserContextServices(this);
-  ShutdownStoragePartitions();
+  // Need to destruct the ResourceContext before posting tasks which may delete
+  // the URLRequestContext because ResourceContext's destructor will remove any
+  // outstanding request while URLRequestContext's destructor ensures that there
+  // are no more outstanding requests.
   if (resource_context_) {
     BrowserThread::DeleteSoon(
       BrowserThread::IO, FROM_HERE, resource_context_.release());
   }
+  ShutdownStoragePartitions();
 }
 
 void ShellBrowserContext::InitWhileIOAllowed() {