Create TimeBase for time related classes.

src/base/platform/time.cc

Index: src/base/platform/time.cc
diff --git a/src/base/platform/time.cc b/src/base/platform/time.cc
index 6d5e538970cfd8e8b3608c196b79c361a44c4107..fed39fc9f74649d09ec8e667bec84387a4237bfe 100644
--- a/src/base/platform/time.cc
+++ b/src/base/platform/time.cc
@@ -28,6 +28,37 @@
 namespace v8 {
 namespace base {
 
+namespace time_internal {
+
+int64_t SaturatedAdd(TimeDelta delta, int64_t value) {
+  CheckedNumeric<int64_t> rv(delta.delta_);
+  rv += value;
+  return FromCheckedNumeric(rv);
+}
+
+int64_t SaturatedSub(TimeDelta delta, int64_t value) {
+  CheckedNumeric<int64_t> rv(delta.delta_);
+  rv -= value;
+  return FromCheckedNumeric(rv);
+}
+
+int64_t FromCheckedNumeric(const CheckedNumeric<int64_t> value) {
+  if (value.IsValid())
+    return value.ValueUnsafe();
+
+  // We could return max/min but we don't really expose what the maximum delta
+  // is. Instead, return max/(-max), which is something that clients can reason
+  // about.
+  // TODO(rvargas) crbug.com/332611: don't use internal values.
+  int64_t limit = std::numeric_limits<int64_t>::max();
+  if (value.validity() == internal::RANGE_UNDERFLOW)
+    limit = -limit;
+  return value.ValueOrDefault(limit);
+}
+
+}  // namespace time_internal
+
+
 TimeDelta TimeDelta::FromDays(int days) {
   return TimeDelta(days * Time::kMicrosecondsPerDay);
 }