Fix geolocation mock to calculate the correct epoch delta

When calculating the delta between Windows Epoch and Unix Epoch in
geolocation mock, Date constructor (that interpretes
parameters in terms of *local* time) was used for the Windows
epoch (1601-01-01) and Unix epoch (1970-01-01) assuming that the
timezone offset didn't change between 1601 and 1970. That assumption
does not hold any more when ICU is used to take into account
the historical timezone offset changes. As a result,
geolocation-api/timestamp.html test failed when the fix for v8:3547
was landed. (https://chromium-review.googlesource.com/c/v8/v8/+/572148 ).

This CL uses Date.UTC() to avoid the issue and is a pre-requisite
to relanding the above v8 CL.

Cq-Include-Trybots: master.tryserver.blink:linux_trusty_blink_rel;master.tryserver.chromium.linux:linux_layout_tests_layout_ng
Bug: v8:3547, chromium:417640, v8:5714
Test: layout test: geolocation-api/*
Change-Id: Iaf718c2818fa9a5f5c64136a38579a1fcafe7805
Reviewed-on: https://chromium-review.googlesource.com/994343Reviewed-by: Jochen Eisinger <jochen@chromium.org>
Reviewed-by: Reilly Grant <reillyg@chromium.org>
Commit-Queue: Jungshik Shin <jshin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#548095}

third_party/WebKit/LayoutTests/geolocation-api/resources/geolocation-mock.js

@@ -92,10 +92,10 @@ class GeolocationMock {
     // device.mojom.Geoposition represents the value of microseconds since the
     // Windows FILETIME epoch (1601-01-01 00:00:00 UTC). So add the delta when
     // sets the |internalValue|. See more info in //base/time/time.h.
-    const windowsEpoch = new Date(1601,1,1,0,0,0,0);
-    const unixEpoch = new Date(1970,1,1,0,0,0,0);
+    const windowsEpoch = Date.UTC(1601,0,1,0,0,0,0);
+    const unixEpoch = Date.UTC(1970,0,1,0,0,0,0);
     // |epochDeltaInMs| equals to base::Time::kTimeTToMicrosecondsOffset.
-    const epochDeltaInMs = unixEpoch.getTime() - windowsEpoch.getTime();
+    const epochDeltaInMs = unixEpoch - windowsEpoch;
 
     this.geoposition_.timestamp.internalValue =
         (new Date().getTime() + epochDeltaInMs)  * 1000;

third_party/WebKit/LayoutTests/geolocation-api/timestamp.html

@@ -37,6 +37,10 @@ function checkPosition(p) {
         debug("  t = " + t);
     }
     shouldBeTrue('t <= then + 1'); // Avoid rounding errors
+    if (t > then + 1) {
+        debug("  t = " + t);
+        debug("  then + 1 = " + (then + 1));
+    }
     finishJSTest();
 }