[ios] Refactor SessionServiceIOS to remove dependency on BrowserState.

ios/chrome/browser/test/perf_test_with_bvc_ios.mm

Index: ios/chrome/browser/test/perf_test_with_bvc_ios.mm
diff --git a/ios/chrome/browser/test/perf_test_with_bvc_ios.mm b/ios/chrome/browser/test/perf_test_with_bvc_ios.mm
index 71faaabb042af4e0a7dc5d76e2a9379640eee21a..3c7b316515c7ea383a58cbb768736957d99d350d 100644
--- a/ios/chrome/browser/test/perf_test_with_bvc_ios.mm
+++ b/ios/chrome/browser/test/perf_test_with_bvc_ios.mm
@@ -116,8 +116,12 @@ void PerfTestWithBVC::SetUp() {
       chrome_browser_state_.get());
 
   // Use the session to create a window which will contain the tab models.
-  SessionWindowIOS* sessionWindow = [[SessionServiceIOS sharedService]
-      loadWindowForBrowserState:chrome_browser_state_.get()];
+  SessionServiceIOS* session_service = [SessionServiceIOS sharedService];
+  NSString* state_path = base::SysUTF8ToNSString(
+      chrome_browser_state_->GetStatePath().AsUTF8Unsafe());
+  NSString* session_path = [session_service sessionPathForDirectory:state_path];
+  SessionWindowIOS* sessionWindow =
+      [session_service loadSessionWindowFromPath:session_path];
 
   // Tab models. The off-the-record (OTR) tab model is required for the stack
   // view controller, which is created in OpenStackView().