Bug 209468

I'm currently at r258908, but I noticed this earlier, using WebKitGTK+. Steps:
a) run MiniBrowser under valgrind
   $ export GIGACAGE_ENABLED=0
   $ G_SLICE=always-malloc valgrind --show-leak-kinds=definite --num-callers=30 --leak-check=no --aspace-minaddr=0x100000000 --track-origins=yes ./MiniBrowser
b) right-click in the body and pick "Inspect Element"

This shows on console:

==16894== Conditional jump or move depends on uninitialised value(s)
==16894==    at 0x10123C193: WebKit::InspectorBrowserAgent::enable(WTF::String&) (InspectorBrowserAgent.cpp:69)
==16894==    by 0x104FA215D: Inspector::BrowserBackendDispatcher::enable(long, WTF::RefPtr<WTF::JSONImpl::Object, WTF::DumbPtrTraits<WTF::JSONImpl::Object> >&&) (InspectorBackendDispatchers.cpp:560)
==16894==    by 0x104FA1F7B: Inspector::BrowserBackendDispatcher::dispatch(long, WTF::String const&, WTF::Ref<WTF::JSONImpl::Object, WTF::DumbPtrTraits<WTF::JSONImpl::Object> >&&) (InspectorBackendDispatchers.cpp:542)
==16894==    by 0x104F9E609: Inspector::BackendDispatcher::dispatch(WTF::String const&) (InspectorBackendDispatcher.cpp:180)
==16894==    by 0x100F4C215: callMemberFunctionImpl<WebKit::WebInspectorProxy, void (WebKit::WebInspectorProxy::*)(const WTF::String &), std::tuple<WTF::String>, 0> (HandleMessage.h:41)
==16894==    by 0x100F4C215: callMemberFunction<WebKit::WebInspectorProxy, void (WebKit::WebInspectorProxy::*)(const WTF::String &), std::tuple<WTF::String>, std::integer_sequence<unsigned long, 0> > (HandleMessage.h:47)
==16894==    by 0x100F4C215: handleMessage<Messages::WebInspectorProxy::SendMessageToBackend, WebKit::WebInspectorProxy, void (WebKit::WebInspectorProxy::*)(const WTF::String &)> (HandleMessage.h:114)
==16894==    by 0x100F4C215: WebKit::WebInspectorProxy::didReceiveMessage(IPC::Connection&, IPC::Decoder&) (WebInspectorProxyMessageReceiver.cpp:55)
==16894==    by 0x101082B4A: IPC::MessageReceiverMap::dispatchMessage(IPC::Connection&, IPC::Decoder&) (MessageReceiverMap.cpp:123)
==16894==    by 0x101162059: didReceiveMessage (WebProcessProxy.cpp:751)
==16894==    by 0x101162059: non-virtual thunk to WebKit::WebProcessProxy::didReceiveMessage(IPC::Connection&, IPC::Decoder&) (WebProcessProxy.cpp:0)
==16894==    by 0x10107B86A: IPC::Connection::dispatchMessage(std::unique_ptr<IPC::Decoder, std::default_delete<IPC::Decoder> >) (Connection.cpp:1077)
==16894==    by 0x10107AD2A: IPC::Connection::dispatchIncomingMessages() (Connection.cpp:1181)
==16894==    by 0x105650358: operator() (Lock.h:84)
==16894==    by 0x105650358: WTF::RunLoop::performWork() (RunLoop.cpp:119)
==16894==    by 0x10569FA15: operator() (RunLoopGLib.cpp:68)
==16894==    by 0x10569FA15: WTF::RunLoop::RunLoop()::$_0::__invoke(void*) (RunLoopGLib.cpp:67)
==16894==    by 0x10413A139: g_main_dispatch (gmain.c:3202)
==16894==    by 0x10413B02F: g_main_context_dispatch (gmain.c:3867)
==16894==    by 0x10413B214: g_main_context_iterate (gmain.c:3940)
==16894==    by 0x10413B63B: g_main_loop_run (gmain.c:4136)
==16894==    by 0x1037881AC: gtk_main (gtkmain.c:1323)
==16894==    by 0x416539: main (main.c:649)
==16894==  Uninitialised value was created by a heap allocation
==16894==    at 0x10083880B: malloc (vg_replace_malloc.c:309)
==16894==    by 0x105642525: WTF::fastMalloc(unsigned long) (FastMalloc.cpp:201)
==16894==    by 0x10110F05D: operator new (WebPageInspectorController.h:49)
==16894==    by 0x10110F05D: make_unique<WebKit::WebPageInspectorController, WebKit::WebPageProxy &> (unique_ptr.h:849)
==16894==    by 0x10110F05D: makeUnique<WebKit::WebPageInspectorController, WebKit::WebPageProxy &> (StdLibExtras.h:483)
==16894==    by 0x10110F05D: WebKit::WebPageProxy::WebPageProxy(WebKit::PageClient&, WebKit::WebProcessProxy&, WTF::Ref<API::PageConfiguration, WTF::DumbPtrTraits<API::PageConfiguration> >&&) (WebPageProxy.cpp:476)
==16894==    by 0x10115AF50: create (WebPageProxy.cpp:428)
==16894==    by 0x10115AF50: createWebPage (WebProcessProxy.cpp:465)
==16894==    by 0x10115AF50: WebKit::WebProcessPool::createWebPage(WebKit::PageClient&, WTF::Ref<API::PageConfiguration, WTF::DumbPtrTraits<API::PageConfiguration> >&&) (WebProcessPool.cpp:1288)
==16894==    by 0x10120D27E: webkitWebViewBaseCreateWebPage(_WebKitWebViewBase*, WTF::Ref<API::PageConfiguration, WTF::DumbPtrTraits<API::PageConfiguration> >&&) (WebKitWebViewBase.cpp:1503)
==16894==    by 0x1011EA75D: webkitWebContextCreatePageForWebView(_WebKitWebContext*, _WebKitWebView*, _WebKitUserContentManager*, _WebKitWebView*) (WebKitWebContext.cpp:1818)
==16894==    by 0x1011F6D0D: webkitWebViewConstructed(_GObject*) (WebKitWebView.cpp:758)
==16894==    by 0x10409D3A0: g_object_new_internal (gobject.c:1999)
==16894==    by 0x10409E138: g_object_new_valist (gobject.c:2287)
==16894==    by 0x10409CE0D: g_object_new (gobject.c:1797)
==16894==    by 0x41694E: createBrowserTab (main.c:81)
==16894==    by 0x4164B6: main (main.c:632)