Add, test, and use clock utilities

util/misc/clock.h

Index: util/misc/clock.h
diff --git a/util/misc/clock.h b/util/misc/clock.h
new file mode 100644
index 0000000000000000000000000000000000000000..88bdcd508c16d3bbed1def82b08b1c44c22e2306
--- /dev/null
+++ b/util/misc/clock.h
@@ -0,0 +1,46 @@
+// 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_MISC_CLOCK_H_
+#define CRASHPAD_UTIL_MISC_CLOCK_H_
+
+#include <stdint.h>
+
+namespace crashpad {
+
+//! \brief Returns the value of the system’s monotonic clock.
+//!
+//! The monotonic clock is a tick counter whose epoch is unspecified. It is a
+//! monotonically-increasing clock that cannot be set, and never jumps backwards
+//! on a running system. The monotonic clock may stop while the system is
+//! sleeping, and it may be reset when the system starts up. This clock is
+//! suitable for computing durations of events. Subject to the underlying
+//! clock’s resolution, successive calls to this function will result in a
+//! series of increasing values.
+//!
+//! \return The value of the system’s monotonic clock, in nanoseconds.
+uint64_t ClockMonotonicNanoseconds();
+
+//! \brief Sleeps for the specified duration.
+//!
+//! \param[in] nanoseconds The number of nanoseconds to sleep. The actual sleep
+//!     may be slightly longer due to latencies and timer resolution.
+//!
+//! This function is resilient against the underlying `nanosleep()` system call
+//! being interrupted by a signal.
+void SleepNanoseconds(uint64_t nanoseconds);
+
+}  // namespace crashpad
+
+#endif  // CRASHPAD_UTIL_MISC_CLOCK_H_