Long tasks: do not clamp times

This CL drops clamping for long tasks to improve accuracy.
Discussion at https://github.com/w3c/longtasks/issues/29

Bug: chromium:681718
Change-Id: If6df344f0203f7b6347f54ffa49be8d6689b7d71
Reviewed-on: https://chromium-review.googlesource.com/587590Reviewed-by: Shubhie Panicker <panicker@chromium.org>
Reviewed-by: Steve Kobes <skobes@chromium.org>
Commit-Queue: Nicolás Peña <npm@chromium.org>
Cr-Commit-Position: refs/heads/master@{#491166}

third_party/WebKit/LayoutTests/external/wpt/longtask-timing/longtask-attributes.html

@@ -19,8 +19,6 @@
             assert_equals(longtask.entryType, "longtask");
             assert_equals(longtask.name, "same-origin-self");
             assert_greater_than(longtask.duration, 50);
-            assert_equals(longtask.startTime, Math.floor(longtask.startTime),
-                "startTime expected to have 1 millisecond granularity");
 
             // Assert the TaskAttributionTiming entry in attribution.
             assert_equals(longtask.attribution.length, 1,

third_party/WebKit/LayoutTests/external/wpt/longtask-timing/longtask-in-externalscript.html

@@ -20,8 +20,6 @@
             assert_equals(longtask.entryType, "longtask");
             assert_equals(longtask.name, "same-origin-self");
             assert_greater_than(longtask.duration, 50);
-            assert_equals(longtask.startTime, Math.floor(longtask.startTime),
-                "startTime expected to have 1 millisecond granularity");
 
             // Assert the TaskAttributionTiming entry in attribution.
             assert_equals(longtask.attribution.length, 1,

third_party/WebKit/LayoutTests/http/tests/performance-timing/longtask/longtask-attributes.html

@@ -13,8 +13,6 @@ async_test(function (t) {
             assert_equals(longtask.entryType, "longtask");
             assert_equals(longtask.name, "self");
             assert_greater_than(longtask.duration, 50);
-            assert_equals(longtask.startTime, Math.floor(longtask.startTime),
-                "startTime expected to have 1 miillisecond granularity");
 
             // Assert the TaskAttributionTiming entry in attribution.
             assert_equals(longtask.attribution.length, 1,

third_party/WebKit/LayoutTests/http/tests/performance-timing/longtask/longtask-externalscript.html

@@ -14,8 +14,6 @@ async_test(function (t) {
             assert_equals(longtask.entryType, "longtask");
             assert_equals(longtask.name, "self");
             assert_greater_than(longtask.duration, 50);
-            assert_equals(longtask.startTime, Math.floor(longtask.startTime),
-                "startTime expected to have 1 miillisecond granularity");
 
             // Assert the TaskAttributionTiming entry in attribution.
             assert_equals(longtask.attribution.length, 1,

third_party/WebKit/LayoutTests/http/tests/performance-timing/longtask/longtask-raf.html

@@ -14,8 +14,6 @@ async_test(function (t) {
             assert_equals(longtask.entryType, "longtask");
             assert_equals(longtask.name, "self");
             assert_greater_than(longtask.duration, 50);
-            assert_equals(longtask.startTime, Math.floor(longtask.startTime),
-                "startTime expected to have 1 miillisecond granularity");
 
             // Assert the TaskAttributionTiming entry in attribution.
             assert_equals(longtask.attribution.length, 1,

third_party/WebKit/Source/core/timing/PerformanceLongTaskTiming.cpp

@@ -9,15 +9,6 @@
 
 namespace blink {
 
-namespace {
-
-double ClampToMillisecond(double time_in_millis) {
-  // Long task times are clamped to 1 millisecond for security.
-  return floor(time_in_millis);
-}
-
-}  // namespace
-
 // static
 PerformanceLongTaskTiming* PerformanceLongTaskTiming::Create(
     double start_time,
@@ -36,10 +27,7 @@ PerformanceLongTaskTiming::PerformanceLongTaskTiming(double start_time,
                                                      String culprit_frame_src,
                                                      String culprit_frame_id,
                                                      String culprit_frame_name)
-    : PerformanceEntry(name,
-                       "longtask",
-                       ClampToMillisecond(start_time),
-                       ClampToMillisecond(end_time)) {
+    : PerformanceEntry(name, "longtask", start_time, end_time) {
   // Only one possible task type exists currently: "script"
   // Only one possible container type exists currently: "iframe"
   TaskAttributionTiming* attribution_entry =