Rename the current CEF runtime to Alloy (see issue #2969)

As part of introducing the Chrome runtime we now need to distinguish
between the classes that implement the current CEF runtime and the
classes the implement the shared CEF library/runtime structure and
public API. We choose the name Alloy for the current CEF runtime
because it describes a combination of Chrome and other elements.

Shared CEF library/runtime classes will continue to use the Cef
prefix. Classes that implement the Alloy or Chrome runtime will use
the Alloy or Chrome prefixes respectively. Classes that extend an
existing Chrome-prefixed class will add the Cef or Alloy suffix,
thereby following the existing naming pattern of Chrome-derived
classes.

This change applies the new naming pattern to an initial set of
runtime-related classes. Additional classes/files will be renamed
and moved as the Chrome runtime implementation progresses.

libcef/browser/extensions/extension_system.cc

@@ -224,7 +224,7 @@ void CefExtensionSystem::Init() {
   //    WebContents routing IDs with the owner CefBrowser. MimeHandlerViewGuest
   //    then loads the extension URL (index.html) in the guest WebContents.
   // 13.Creation of the RenderFrame in the guest renderer process triggers a
-  //    sync IPC call from CefContentRendererClient::MaybeCreateBrowser to
+  //    sync IPC call from AlloyContentRendererClient::MaybeCreateBrowser to
   //    CefBrowserInfoManager::GetBrowserInfo in the browser process to retrieve
   //    the CefBrowser information, which will be immediately available due to
   //    step 12.
@@ -248,7 +248,7 @@ void CefExtensionSystem::Init() {
   // 17.HTMLPlugInElement::RequestObject is called in the guest renderer process
   //    and determines that the PDF PPAPI plugin should be handled internally
   //    (handled_externally=false). A PluginDocument is created and
-  //    CefContentRendererClient::OverrideCreatePlugin is called to create a
+  //    AlloyContentRendererClient::OverrideCreatePlugin is called to create a
   //    WebPlugin.
   // 18.The PDF extension and PDF plugin are now loaded. Print commands, if
   //    any, are handled in the guest renderer process by ChromePDFPrintClient