Fix a memory leak found by clang static analyzer.

ios/web/navigation/crw_session_controller.mm

Index: ios/web/navigation/crw_session_controller.mm
diff --git a/ios/web/navigation/crw_session_controller.mm b/ios/web/navigation/crw_session_controller.mm
index c5078c9d9e8d4d4df37908eaf4af2722133887ab..ff1093b43781781ba5eac0e190de40127bde9325 100644
--- a/ios/web/navigation/crw_session_controller.mm
+++ b/ios/web/navigation/crw_session_controller.mm
@@ -843,6 +843,8 @@ NSString* const kXCallbackParametersKey = @"xCallbackParameters";
 - (NSString*)uniqueID {
   CFUUIDRef uuidRef = CFUUIDCreate(NULL);
   CFStringRef uuidStringRef = CFUUIDCreateString(NULL, uuidRef);
+  CFRelease(uuidRef);

[Eugene But (OOO till 7-30), 2016/09/20 21:59:40]

How about simply: |return [NSUUID NSUUID].UUIDString;|

[sdefresne, 2016/09/21 09:19:08]

I'll leave this to you as owners of the code to decide whether you want to
rewrite it from using CoreFoundation to using NS objects.

+
   NSString* uuid =
       [NSString stringWithString:base::mac::ObjCCastStrict<NSString>(
                                      CFBridgingRelease(uuidStringRef))];