Bug 1952623 - Part 3: Avoid unnecessary to nanoseconds conversion. r=mgaudet

Drive-by change:
- `SystemUTCEpochNanoseconds` is infallible, so we can return the result
  directly and don't need an out-param.

Differential Revision: https://phabricator.services.mozilla.com/D244550

UltraBlame original commit: 225df4261b1c4cd2083ef3f5951cbe14c9145a77

Author: marco-c

js/src/builtin/temporal/TemporalNow.cpp

@@ -402,15 +402,12 @@ SystemUTCEpochNanoseconds
 *
 /
 static
-bool
-SystemUTCEpochNanoseconds
+int64_t
+SystemUTCEpochMilliseconds
 (
 JSContext
 *
 cx
-EpochNanoseconds
-*
-result
 )
 {
 /
@@ -475,14 +472,7 @@ EndOfTime
 Step
 3
 .
-*
-result
-=
-EpochNanoseconds
-:
-:
-fromMilliseconds
-(
+return
 int64_t
 (
 nowMillis
@@ -491,10 +481,37 @@ toDouble
 (
 )
 )
-)
 ;
+}
+/
+*
+*
+*
+SystemUTCEpochNanoseconds
+(
+)
+*
+/
+static
+EpochNanoseconds
+SystemUTCEpochNanoseconds
+(
+JSContext
+*
+cx
+)
+{
 return
-true
+EpochNanoseconds
+:
+:
+fromMilliseconds
+(
+SystemUTCEpochMilliseconds
+(
+cx
+)
+)
 ;
 }
 /
@@ -566,38 +583,19 @@ applicable
 Step
 3
 .
-EpochNanoseconds
-epochNs
-;
-if
-(
-!
-SystemUTCEpochNanoseconds
+int64_t
+epochMillis
+=
+SystemUTCEpochMilliseconds
 (
 cx
-&
-epochNs
 )
-)
-{
-return
-false
 ;
-}
 /
 /
 Step
 4
 .
-int64_t
-epochMillis
-=
-epochNs
-.
-floorToMilliseconds
-(
-)
-;
 int32_t
 offsetMillis
 =
@@ -652,7 +650,13 @@ dateTime
 =
 GetISODateTimeFor
 (
-epochNs
+EpochNanoseconds
+:
+:
+fromMilliseconds
+(
+epochMillis
+)
 offsetMillis
 *
 ToNanoseconds
@@ -703,24 +707,14 @@ false
 Step
 3
 .
-EpochNanoseconds
+auto
 epochNs
-;
-if
-(
-!
+=
 SystemUTCEpochNanoseconds
 (
 cx
-&
-epochNs
 )
-)
-{
-return
-false
 ;
-}
 /
 /
 Step
@@ -852,24 +846,14 @@ vp
 Step
 1
 .
-EpochNanoseconds
+auto
 epochNs
-;
-if
-(
-!
+=
 SystemUTCEpochNanoseconds
 (
 cx
-&
-epochNs
-)
 )
-{
-return
-false
 ;
-}
 /
 /
 Step
@@ -1146,24 +1130,14 @@ false
 Step
 3
 .
-EpochNanoseconds
+auto
 epochNs
-;
-if
-(
-!
+=
 SystemUTCEpochNanoseconds
 (
 cx
-&
-epochNs
 )
-)
-{
-return
-false
 ;
-}
 /
 /
 Step