Provide a user default that can be used to disable docking of the Web Inspector.

The user default is "WebKit Web Inspector Setting - inspectorAttachDisabled".

https://webkit.org/b/113779
rdar://problem/13446021

Reviewed by Joseph Pecoraro.

Source/WebKit/cf:

* WebCoreSupport/WebInspectorClientCF.cpp:
(WebInspectorClient::inspectorAttachDisabled): Added.
(WebInspectorClient::setInspectorAttachDisabled): Added.

Source/WebKit/mac:

* WebCoreSupport/WebInspectorClient.h:
(WebInspectorClient::inspectorAttachDisabled): Added.
(WebInspectorClient::setInspectorAttachDisabled): Added.

* WebCoreSupport/WebInspectorClient.mm:
(WebInspectorClient::didResizeMainFrame):
(-[WebInspectorWindowController window]):
(-[WebInspectorWindowController showWindow:]):
Check inspectorAttachDisabled() in places where we attach or update the dock button.

Source/WebKit/win:

* WebCoreSupport/WebInspectorClient.h:
(WebInspectorClient::inspectorAttachDisabled): Added.
(WebInspectorClient::setInspectorAttachDisabled): Added.


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@147482 268f45cc-cd09-0410-ab3c-d52691b4dbfc