Fixit: Fork base::TimeTicks --> TimeTicks + ThreadTicks + TraceTicks

TimeTicks was being overused for time values from three different clock
sources.  This change splits the class into three separate classes: The
general-purpose monotonic time (TimeTicks), the thread-local run time
(ThreadTicks), and the global system trace time (TraceTicks).  With this
change, the compiler is now able to use type-checking to guarantee
values from different clocks are not being mixed when doing time math.

This is the 2nd in a two-part change.  Part 1 factored-out the
comparison and math operator overloads common to base::Time and
base::TimeTicks into a templated base class.  The new ThreadTicks and
TraceTicks time classes also inherit from that base class.

Updated base/trace_event/* and a handful of outside-of-base uses of
ThreadNow() and NowFromSystemTraceTime() to use the new classes.  A bug
was identified and fixed, in src/ui/gl/angle_platform_impl.cc, where
values from TimeTicks::Now() were being erroneously provided to
base::TraceEvent instead of values from NowFromSystemTraceTime().

BUG=467417
CQ_INCLUDE_TRYBOTS=tryserver.blink:linux_blink_rel
NOTRY=true

Review URL: https://codereview.chromium.org/1122153002

Cr-Commit-Position: refs/heads/master@{#332080}

1 files changed, 10 insertions, 10 deletions

diff --git a/cc/debug/rendering_stats_instrumentation.cc b/cc/debug/rendering_stats_instrumentation.cc
index 7497c62..315743b 100644
--- a/cc/debug/rendering_stats_instrumentation.cc
+++ b/cc/debug/rendering_stats_instrumentation.cc
@@ -37,21 +37,21 @@ void RenderingStatsInstrumentation::AccumulateAndClearImplThreadStats() {
   impl_thread_rendering_stats_ = RenderingStats();
 }
 
-base::TimeTicks RenderingStatsInstrumentation::StartRecording() const {
+base::TimeDelta RenderingStatsInstrumentation::StartRecording() const {
   if (record_rendering_stats_) {
-    if (base::TimeTicks::IsThreadNowSupported())
-      return base::TimeTicks::ThreadNow();
-    return base::TimeTicks::Now();
+    if (base::ThreadTicks::IsSupported())
+      return base::ThreadTicks::Now() - base::ThreadTicks();
+    return base::TimeTicks::Now() - base::TimeTicks();
   }
-  return base::TimeTicks();
+  return base::TimeDelta();
 }
 
 base::TimeDelta RenderingStatsInstrumentation::EndRecording(
-    base::TimeTicks start_time) const {
-  if (!start_time.is_null()) {
-    if (base::TimeTicks::IsThreadNowSupported())
-      return base::TimeTicks::ThreadNow() - start_time;
-    return base::TimeTicks::Now() - start_time;
+    base::TimeDelta start_time) const {
+  if (start_time != base::TimeDelta()) {
+    if (base::ThreadTicks::IsSupported())
+      return (base::ThreadTicks::Now() - base::ThreadTicks()) - start_time;
+    return (base::TimeTicks::Now() - base::TimeTicks()) - start_time;
   }
   return base::TimeDelta();
 }