[ObjC ARC] Converts ios/web:web to ARC.

ios/web/web_state/ui/wk_web_view_configuration_provider.mm

Index: ios/web/web_state/ui/wk_web_view_configuration_provider.mm
diff --git a/ios/web/web_state/ui/wk_web_view_configuration_provider.mm b/ios/web/web_state/ui/wk_web_view_configuration_provider.mm
index 7527133963eaf71a5d883e8b9da24a8d72e6df5a..209746341d51ce18344f1a7e7b68b8e944b77421 100644
--- a/ios/web/web_state/ui/wk_web_view_configuration_provider.mm
+++ b/ios/web/web_state/ui/wk_web_view_configuration_provider.mm
@@ -14,6 +14,10 @@
 #import "ios/web/web_state/js/page_script_util.h"
 #import "ios/web/web_state/ui/crw_wk_script_message_router.h"
 
+#if !defined(__has_feature) || !__has_feature(objc_arc)
+#error "This file requires ARC support."
+#endif
+
 namespace web {
 
 namespace {
@@ -23,10 +27,10 @@ const char kWKWebViewConfigProviderKeyName[] = "wk_web_view_config_provider";
 // Returns an autoreleased instance of WKUserScript to be added to
 // configuration's userContentController.
 WKUserScript* InternalGetEarlyPageScript(BrowserState* browser_state) {
-  return [[[WKUserScript alloc]
+  return [[WKUserScript alloc]
         initWithSource:GetEarlyPageScript(browser_state)
          injectionTime:WKUserScriptInjectionTimeAtDocumentStart
-      forMainFrameOnly:YES] autorelease];
+      forMainFrameOnly:YES];
 }
 
 }  // namespace
@@ -70,7 +74,7 @@ WKWebViewConfigurationProvider::GetWebViewConfiguration() {
         addUserScript:InternalGetEarlyPageScript(browser_state_)];
   }
   // Prevent callers from changing the internals of configuration.
-  return [[configuration_ copy] autorelease];
+  return [configuration_ copy];
 }
 
 CRWWKScriptMessageRouter*
@@ -88,9 +92,16 @@ WKWebViewConfigurationProvider::GetScriptMessageRouter() {
 void WKWebViewConfigurationProvider::Purge() {
   DCHECK([NSThread isMainThread]);
 #if DCHECK_IS_ON()
-  base::WeakNSObject<id> weak_configuration(configuration_);
-  base::WeakNSObject<id> weak_router(router_);
-  base::WeakNSObject<id> weak_process_pool([configuration_ processPool]);
+  base::WeakNSObject<id> weak_configuration;
+  base::WeakNSObject<id> weak_router;
+  // It's expected that the weak objects auto-nil by the end of this method.
+  // They should not be in any autoreleasepool that might keep them alive.
+  @autoreleasepool {
+    weak_configuration.reset(configuration_);
+    weak_router.reset(router_);
+  }
+// TODO(crbug.com/522672): See commented out DCHECK below.
+// __weak id weak_process_pool = [configuration_ processPool];
 #endif  // DCHECK_IS_ON()
   configuration_.reset();
   router_.reset();