Remove `Runnable` concept from base/bind_internal.h

`Runnable` concept was useful when bind_internal.h was a huge generated
file. However, it's an unneeded layer these days.
This CL removes `Runnable` from bind_internal.h to simplify its impl.
After this CL, BindState holds the bound Functor directly in its internal
storage.

This CL contains:
 * Merge bind_internal_win.h into bind_internal.h
 * Move typechecks in Bind() into MakeBindStateType.
 * Remove no longer used HasIsMethodTag in bind_helper.h.
 * Remove InvokeHelper specialization for IgnoreResult.
 * Merge assertion-only InvokeHelper specialization into another
   specialization.
 * Factor out the type setup in BindState into MakeBindStateType.

BUG=554299

Review-Url: https://codereview.chromium.org/2106773002
Cr-Commit-Position: refs/heads/master@{#403413}

diff --git a/base/bind.h b/base/bind.h
index ed5a94a..9cf65b6 100644
--- a/base/bind.h
+++ b/base/bind.h

@@ -21,55 +21,19 @@
 // If you're reading the implementation, before proceeding further, you should
 // read the top comment of base/bind_internal.h for a definition of common
 // terms and concepts.
-//
-// RETURN TYPES
-//
-// Though Bind()'s result is meant to be stored in a Callback<> type, it
-// cannot actually return the exact type without requiring a large amount
-// of extra template specializations. The problem is that in order to
-// discern the correct specialization of Callback<>, Bind would need to
-// unwrap the function signature to determine the signature's arity, and
-// whether or not it is a method.
-//
-// Each unique combination of (arity, function_type, num_prebound) where
-// function_type is one of {function, method, const_method} would require
-// one specialization.  We eventually have to do a similar number of
-// specializations anyways in the implementation (see the Invoker<>,
-// classes).  However, it is avoidable in Bind if we return the result
-// via an indirection like we do below.
-//
-// TODO(ajwong): We might be able to avoid this now, but need to test.
-//
-// It is possible to move most of the static_assert into BindState<>, but it
-// feels a little nicer to have the asserts here so people do not need to crack
-// open bind_internal.h.  On the other hand, it makes Bind() harder to read.
 
 namespace base {
 
 template <typename Functor, typename... Args>
-inline base::Callback<MakeUnboundRunType<Functor, Args...>>
-Bind(Functor functor, Args&&... args) {
-  // Type aliases for how to store and run the functor.
-  using RunnableType = typename internal::FunctorTraits<Functor>::RunnableType;
-
-  const bool is_method = internal::HasIsMethodTag<RunnableType>::value;
-
-  // For methods, we need to be careful for parameter 1.  We do not require
-  // a scoped_refptr because BindState<> itself takes care of AddRef() for
-  // methods. We also disallow binding of an array as the method's target
-  // object.
-  static_assert(!internal::BindsArrayToFirstArg<is_method, Args...>::value,
-                "first bound argument to method cannot be array");
-  static_assert(
-      !internal::HasRefCountedParamAsRawPtr<is_method, Args...>::value,
-      "a parameter is a refcounted type and needs scoped_refptr");
-
-  using BindState = internal::BindState<RunnableType, Args...>;
+inline base::Callback<MakeUnboundRunType<Functor, Args...>> Bind(
+    Functor&& functor,
+    Args&&... args) {
+  using BindState = internal::MakeBindStateType<Functor, Args...>;
   using UnboundRunType = MakeUnboundRunType<Functor, Args...>;
-  using CallbackType = Callback<UnboundRunType>;
   using Invoker = internal::Invoker<BindState, UnboundRunType>;
 
-  return CallbackType(new BindState(internal::MakeRunnable(functor),
+  using CallbackType = Callback<UnboundRunType>;
+  return CallbackType(new BindState(std::forward<Functor>(functor),
                                     std::forward<Args>(args)...),
                       &Invoker::Run);
 }