[include-cleaner] Add a unique_ptr-style member expr test in WalkASTTest.

[hokein]

Summary

This is a test I missed to mention in https://reviews.llvm.org/D139087.

[VitaNuo]

Thank you!

clang-tools-extra/include-cleaner/unittests/WalkASTTest.cpp

200

Should "struct unique_ptr` go on the next line mayber? At least that's how I have seen templates defined until now :)

clang-tools-extra/include-cleaner/unittests/WalkASTTest.cpp

TEST(WalkAST, MemberExprs) {
   testWalk("struct Base { int a; }; struct $explicit^Derived : public Base {};",
            "void fun(Derived& d) { d.^a; }");
   testWalk("struct Base { int a; }; struct $explicit^Derived : public Base {};",
            "void fun() { Derived().^a; }");
   testWalk("struct Base { int a; }; struct $explicit^Derived : public Base {};",
            "Derived foo(); void fun() { foo().^a; }");
   testWalk("struct Base { int a; }; struct $explicit^Derived : public Base {};",
            "Derived& foo(); void fun() { foo().^a; }");
+  testWalk(R"cpp(
+      template <typename T>
+      struct unique_ptr {
+        T *operator->();
+      };
+      struct $explicit^Foo { int a; };)cpp",
+           "void test(unique_ptr<Foo> &V) { V->^a; }");
+  testWalk(R"cpp(
+      template <typename T>
+      struct $explicit^unique_ptr {
+        void release();
+      };
+      struct Foo {};)cpp",
+           "void test(unique_ptr<Foo> &V) { V.^release(); }");
 }
 
 TEST(WalkAST, ConstructExprs) {
   testWalk("struct $implicit^S {};", "S ^t;");
   testWalk("struct S { $implicit^S(); };", "S ^t;");
   testWalk("struct S { $explicit^S(int); };", "S ^t(42);");
   testWalk("struct S { $implicit^S(int); };", "S t = ^42;");
 }