RFR: 8285519: Simplify TimeUnit.convert calls

[Andrey Turbanov]

TimeUnit.toMillis/toNanos/toMicros/toSeconds is shorter and a bit faster.
Compared via JMH benchmark: 150ns -> 125ns/op
<details>
<summary>Benchamark adapted from http://cr.openjdk.java.net/~shade/8152083/TimeUnitBench.java</summary>


@Warmup(iterations = 5, time = 1, timeUnit = TimeUnit.SECONDS)
@Measurement(iterations = 5, time = 1, timeUnit = TimeUnit.SECONDS)
@Fork(1)
@State(Scope.Thread)
@BenchmarkMode(Mode.AverageTime)
@OutputTimeUnit(TimeUnit.NANOSECONDS)
public class TimeUnitBench {

    static final int SIZE = TimeUnit.values().length * 10;

    @Param({"0", "1", "2", "3", "4", "5", "6", "-1"})
    int bias;

    TimeUnit[] mod;

    @Setup
    public void setup() {
        mod = new TimeUnit[SIZE];

        TimeUnit[] vals = TimeUnit.values();
        for (int c = 0; c < SIZE; c++) {
            if (bias == -1) {
                // megamorphic
                mod[c] = vals[c % vals.length];
            } else {
                mod[c] = vals[bias];
            }
        }

        Random r = new Random();
        for (int c = 0; c < 10000; c++) {
            int i = r.nextInt();
            for (int o = 0; o < vals.length; o++) {
                if (vals[o].toNanos(i) != TimeUnit.NANOSECONDS.convert(i, vals[o]))
                    throw new IllegalStateException("switch " + o);
            }
        }
    }

    @Benchmark
    public void const_convert(Blackhole bh) {
        for (TimeUnit tu : mod) {
            bh.consume(do_convert(tu));
        }
    }

    @Benchmark
    public void value_convert(Blackhole bh) {
        for (TimeUnit tu : mod) {
            bh.consume(do_convert(tu, 1L));
        }
    }

    @Benchmark
    public void const_toNanos(Blackhole bh) {
        for (TimeUnit tu : mod) {
            bh.consume(do_toNanos(tu));
        }
    }

    @Benchmark
    public void value_toNanos(Blackhole bh) {
        for (TimeUnit tu : mod) {
            bh.consume(do_toNanos(tu, 1L));
        }
    }

    @CompilerControl(CompilerControl.Mode.DONT_INLINE)
    private long do_toNanos(TimeUnit tu) {
        return tu.toNanos(1L);
    }

    @CompilerControl(CompilerControl.Mode.DONT_INLINE)
    private long do_toNanos(TimeUnit tu, long value) {
        return tu.toNanos(value);
    }

    @CompilerControl(CompilerControl.Mode.DONT_INLINE)
    private long do_convert(TimeUnit tu) {
        return TimeUnit.NANOSECONDS.convert(1L, tu);
    }

    @CompilerControl(CompilerControl.Mode.DONT_INLINE)
    private long do_convert(TimeUnit tu, long value) {
        return TimeUnit.NANOSECONDS.convert(value, tu);
    }
}

Results:

Benchmark                    (bias)  Mode  Cnt    Score    Error  Units
TimeUnitBench.const_convert       0  avgt    5  151,856 ± 28,595  ns/op
TimeUnitBench.const_convert       1  avgt    5  150,720 ± 23,863  ns/op
TimeUnitBench.const_convert       2  avgt    5  151,432 ± 23,184  ns/op
TimeUnitBench.const_convert       3  avgt    5  150,959 ± 24,726  ns/op
TimeUnitBench.const_convert       4  avgt    5  150,966 ± 25,280  ns/op
TimeUnitBench.const_convert       5  avgt    5  150,976 ± 25,542  ns/op
TimeUnitBench.const_convert       6  avgt    5  151,118 ± 25,254  ns/op
TimeUnitBench.const_convert      -1  avgt    5  152,673 ± 29,861  ns/op
TimeUnitBench.const_toNanos       0  avgt    5  121,296 ± 25,236  ns/op
TimeUnitBench.const_toNanos       1  avgt    5  121,707 ± 25,364  ns/op
TimeUnitBench.const_toNanos       2  avgt    5  121,736 ± 25,726  ns/op
TimeUnitBench.const_toNanos       3  avgt    5  121,822 ± 25,491  ns/op
TimeUnitBench.const_toNanos       4  avgt    5  121,867 ± 26,090  ns/op
TimeUnitBench.const_toNanos       5  avgt    5  121,927 ± 25,611  ns/op
TimeUnitBench.const_toNanos       6  avgt    5  121,821 ± 25,843  ns/op
TimeUnitBench.const_toNanos      -1  avgt    5  121,923 ± 25,206  ns/op
TimeUnitBench.value_convert       0  avgt    5  150,525 ± 25,439  ns/op
TimeUnitBench.value_convert       1  avgt    5  151,098 ± 24,024  ns/op
TimeUnitBench.value_convert       2  avgt    5  151,259 ± 25,381  ns/op
TimeUnitBench.value_convert       3  avgt    5  151,030 ± 25,548  ns/op
TimeUnitBench.value_convert       4  avgt    5  151,290 ± 25,998  ns/op
TimeUnitBench.value_convert       5  avgt    5  151,006 ± 25,448  ns/op
TimeUnitBench.value_convert       6  avgt    5  150,945 ± 25,314  ns/op
TimeUnitBench.value_convert      -1  avgt    5  151,186 ± 25,814  ns/op
TimeUnitBench.value_toNanos       0  avgt    5  121,556 ± 25,745  ns/op
TimeUnitBench.value_toNanos       1  avgt    5  123,410 ± 22,323  ns/op
TimeUnitBench.value_toNanos       2  avgt    5  125,452 ± 26,575  ns/op
TimeUnitBench.value_toNanos       3  avgt    5  125,297 ± 26,204  ns/op
TimeUnitBench.value_toNanos       4  avgt    5  125,357 ± 26,085  ns/op
TimeUnitBench.value_toNanos       5  avgt    5  125,165 ± 26,185  ns/op
TimeUnitBench.value_toNanos       6  avgt    5  125,536 ± 25,487  ns/op
TimeUnitBench.value_toNanos      -1  avgt    5  125,460 ± 25,063  ns/op


</details>

-------------

Commit messages:
 - [PATCH] Simplify TimeUnit.convert calls to TimeUnit.toSomething instead

Changes: https://git.openjdk.java.net/jdk/pull/8376/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=8376&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8285519
  Stats: 30 lines in 7 files changed: 2 ins; 0 del; 28 mod
  Patch: https://git.openjdk.java.net/jdk/pull/8376.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/8376/head:pull/8376

PR: https://git.openjdk.java.net/jdk/pull/8376