Update the Pass→std::move() tool to handle nested calls to Pass().

tools/clang/pass_to_move/tests/test-original.cc

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 struct A {
   A&& Pass();
 };
 
 struct B {
   B& Pass();
 };
 
 struct C {
   A a;
 };
 
 struct D {
   D&& NotPass();
 };
 
 struct E {
   E() : a(new A) {}
   ~E() { delete a; }
   A* a;
 };
 
-void F() {
+struct F {
+  explicit F(A&&);
+  F&& Pass();
+};
+
+void Test() {
+  // Pass that returns rvalue reference should use std::move.
   A a1;
   A a2 = a1.Pass();
 
+  // Pass that doesn't return a rvalue reference should not be rewritten.
   B b1;
   B b2 = b1.Pass();
 
+  // std::move() needs to wrap the entire expression when passing a member.
   C c;
   A a3 = c.a.Pass();
 
+  // Don't rewrite things that return rvalue references that aren't named Pass.
   D d1;
   D d2 = d1.NotPass();
 
+  // Pass via a pointer type should dereference the pointer first.
   E e;
   A a4 = e.a->Pass();
+
+  // Nested Pass() is handled correctly.
+  A a5;
+  F f = F(a5.Pass()).Pass();
+
+  // Chained Pass is handled (mostly) correctly. The replacement applier dedupes
+  // the insertion of std::move, so the result is not completely correct...
+  // ... but hopefully there's very little code following this broken pattern.
+  A a6;
+  A a7 = a6.Pass().Pass();
 }