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/thread_util.h

@@ -53,8 +53,8 @@
 // Tasks posted with this method are not guaranteed to run sequentially. Use
 // base::CreateSequencedTaskRunner instead if sequence is important.
 // Sequenced runners at various priorities that always execute all pending tasks
-// before shutdown are available via CefContentBrowserClient::*_task_runner()
-// and exposed by the CEF API.
+// before shutdown are available via CefTaskRunnerManager and exposed by the CEF
+// API.
 #define CEF_POST_BLOCKING_TASK(priority, task)                          \
   base::PostTask(                                                       \
       FROM_HERE,                                                        \