Introduce MinidumpWritable, its dependencies, and their tests

util/numeric/safe_assignment.h

Index: util/numeric/safe_assignment.h
diff --git a/util/numeric/safe_assignment.h b/util/numeric/safe_assignment.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_NUMERIC_SAFE_ASSIGNMENT_H_
+#define CRASHPAD_UTIL_NUMERIC_SAFE_ASSIGNMENT_H_
+
+#include "base/numerics/safe_conversions.h"
+
+namespace crashpad {
+
+//! \brief Performs an assignment if it can be done safely, and signals if it
+//!     cannot be done safely.
+//!
+//! \param[out] destination A pointer to the variable to be assigned to.
+//! \param[in] source The value to assign.
+//!
+//! \return `true` if \a source is in the range supported by the type of \a
+//!     *destination, with the assignment to \a *destination having been
+//!     performed. `false` if the assignment cannot be completed safely because
+//!     \a source is outside of this range.
+template <typename Destination, typename Source>
+bool AssignIfInRange(Destination* destination, Source source) {
+  if (!base::IsValueInRangeForNumericType<Destination>(source)) {
+    return false;
+  }
+
+  *destination = source;
+  return true;
+}
+
+}  // namespace crashpad
+
+#endif  // CRASHPAD_UTIL_NUMERIC_SAFE_ASSIGNMENT_H_