[WebKit2] REGRESSION (Custom Protocols): Reproducible crash when navigating to URL with an invalid scheme
https://bugs.webkit.org/show_bug.cgi?id=115790

Reviewed by Alexey Proskuryakov.

Source/WebKit2:

NSMutableSet does not support adding or removing nil objects, and
WTF::HashSet does not support adding, removing, or checking for null
WTF::Strings.

For the NSMutableSet case, make sure that we don't try to add or remove
nil NSStrings.

For the WTF::HashSet case, NSURL will return a nil NSString if we ask
it for its scheme when it is invalid, which we will convert to a null
WTF::String. Don't try to check if our HashSet of registered schemes
contains a null String.

* Shared/Network/CustomProtocols/mac/CustomProtocolManagerMac.mm:
(WebKit::CustomProtocolManager::registerScheme): Assert that the scheme
isn't null. We reject null schemes at the WKBrowsingContextController level.
(WebKit::CustomProtocolManager::unregisterScheme): Ditto.
(WebKit::CustomProtocolManager::supportsScheme): If scheme is null, return false.
* UIProcess/API/mac/WKBrowsingContextController.mm:
(+[WKBrowsingContextController registerSchemeForCustomProtocol:]): Do not register a nil scheme.
(+[WKBrowsingContextController unregisterSchemeForCustomProtocol:]): Ditto.

Tools:

Added two API tests:

1) Verify that +[WKBrowsingContextController (un)registerSchemeForCustomProtocol:] can be called with a nil NSString without crashing.
2) Verify that +[WKCustomProtocol canInitWithRequest:] does not crash when passed an NSURLRequest with an invalid scheme.

* TestWebKitAPI/TestWebKitAPI.xcodeproj/project.pbxproj:
* TestWebKitAPI/Tests/WebKit2ObjC/CustomProtocolsInvalidScheme.mm: Added.
(TestWebKitAPI):
(TestWebKitAPI::TEST):
* TestWebKitAPI/Tests/WebKit2ObjC/CustomProtocolsInvalidScheme_Bundle.cpp: Added.
(TestWebKitAPI):
(TestWebKitAPI::decidePolicyForNavigationAction):
(CustomProtocolInvalidSchemeTest):
(TestWebKitAPI::CustomProtocolInvalidSchemeTest::CustomProtocolInvalidSchemeTest):

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@149774 268f45cc-cd09-0410-ab3c-d52691b4dbfc