Add the MultiprocessExec test and its test

util/test/multiprocess_exec.h

Index: util/test/multiprocess_exec.h
diff --git a/util/test/multiprocess_exec.h b/util/test/multiprocess_exec.h
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+// Copyright 2014 The Crashpad Authors. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#ifndef CRASHPAD_UTIL_TEST_MULTIPROCESS_EXEC_H_
+#define CRASHPAD_UTIL_TEST_MULTIPROCESS_EXEC_H_
+
+#include <string>
+#include <vector>
+
+#include "base/basictypes.h"
+#include "util/test/multiprocess.h"
+
+namespace crashpad {
+namespace test {
+
+//! \brief Manages an `exec()`-based multiprocess test.
+//!
+//! These tests are based on `fork()` and `exec()`. The parent process is able
+//! to communicate with the child in the same manner as a base-class
+//! Multiprocess parent. The read and write pipes appear in the child process on
+//! stdin and stdout, respectively.
+//!
+//! Subclasses are expected to implement the parent in the same was as a
+//! base-class Multiprocess parent. The child must be implemented in an
+//! executable to be set by SetChildCommand().
+class MultiprocessExec : public Multiprocess {
+ public:
+  MultiprocessExec();
+
+  //! \brief Sets the command to `exec()` in the child.
+  //!
+  //! This method must be called before the test can be Run().
+  //!
+  //! \param[in] command The executable’s pathname.
+  //! \param[in] arguments The command-line arguments to pass to the child
+  //!     process in its `argv[]` vector. This vector must begin at `argv[1]`,
+  //!     as \a command is implicitly used as `argv[0]`. This argument may be
+  //!     `NULL` if no command-line arguments are to be passed.
+  void SetChildCommand(const std::string& command,
+                       const std::vector<std::string>* arguments);
+
+ protected:
+  ~MultiprocessExec();
+
+  // Multiprocess:
+  virtual void PreFork() override;
+
+ private:
+  // Multiprocess:
+  virtual void MultiprocessChild() override;
+
+  std::string command_;
+  std::vector<std::string> arguments_;
+  std::vector<const char*> argv_;
+
+  DISALLOW_COPY_AND_ASSIGN(MultiprocessExec);
+};
+
+}  // namespace test
+}  // namespace crashpad
+
+#endif  // CRASHPAD_UTIL_TEST_MULTIPROCESS_EXEC_H_