Add test case for nullptr checks in WebPage::m_activeColorChooser. See Bug 214699: [IPC hardening] Add nullptr checks for WebPage::m_activeColorChooser <https://bugs.webkit.org/show_bug.cgi?id=214699>
<rdar://problem/66061448>
NOTE: Manual test case attached to Bug 148834 reproduces this crash before the fix. Not sure if the Blink layout test attached will do the same. Bug 148834: WTFCrashWithSecurityImplication running Blink layout test fast/forms/color/color-type-change-on-close.html <https://bugs.webkit.org/show_bug.cgi?id=148834>