Add default constructor to relative units types

0 is natural default value for types that can be accumulated
Having default constructor simplify usage of these types in templated code.

Bug: None
Change-Id: If005c69018a2a11011bc789502fdbc600cad3278
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/369440
Reviewed-by: Per Kjellander <perkj@webrtc.org>
Commit-Queue: Danil Chapovalov <danilchap@webrtc.org>
Commit-Queue: Per Kjellander <perkj@webrtc.org>
Reviewed-by: Mirko Bonadei <mbonadei@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#43460}

api/units/data_rate.h

@@ -46,7 +46,7 @@ class DataRate final : public rtc_units_impl::RelativeUnit<DataRate> {
   }
   static constexpr DataRate Infinity() { return PlusInfinity(); }
 
-  DataRate() = delete;
+  constexpr DataRate() = default;
 
   template <typename Sink>
   friend void AbslStringify(Sink& sink, DataRate value);

api/units/data_rate_unittest.cc

@@ -34,6 +34,7 @@ TEST(DataRateTest, ConstExpr) {
   constexpr int64_t kValue = 12345;
   constexpr DataRate kDataRateZero = DataRate::Zero();
   constexpr DataRate kDataRateInf = DataRate::Infinity();
+  static_assert(DataRate() == kDataRateZero);
   static_assert(kDataRateZero.IsZero(), "");
   static_assert(kDataRateInf.IsInfinite(), "");
   static_assert(kDataRateInf.bps_or(-1) == -1, "");

api/units/data_size.h

@@ -29,7 +29,7 @@ class DataSize final : public rtc_units_impl::RelativeUnit<DataSize> {
   }
   static constexpr DataSize Infinity() { return PlusInfinity(); }
 
-  DataSize() = delete;
+  constexpr DataSize() = default;
 
   template <typename Sink>
   friend void AbslStringify(Sink& sink, DataSize value);

api/units/data_size_unittest.cc

@@ -22,6 +22,7 @@ TEST(DataSizeTest, ConstExpr) {
   constexpr int64_t kValue = 12345;
   constexpr DataSize kDataSizeZero = DataSize::Zero();
   constexpr DataSize kDataSizeInf = DataSize::Infinity();
+  static_assert(DataSize() == kDataSizeZero);
   static_assert(kDataSizeZero.IsZero(), "");
   static_assert(kDataSizeInf.IsInfinite(), "");
   static_assert(kDataSizeInf.bytes_or(-1) == -1, "");

api/units/frequency.h

@@ -41,7 +41,7 @@ class Frequency final : public rtc_units_impl::RelativeUnit<Frequency> {
     return FromFraction(1'000'000, value);
   }
 
-  Frequency() = delete;
+  constexpr Frequency() = default;
 
   template <typename Sink>
   friend void AbslStringify(Sink& sink, Frequency value);

api/units/frequency_unittest.cc

@@ -20,6 +20,7 @@ TEST(FrequencyTest, ConstExpr) {
   constexpr Frequency kFrequencyZero = Frequency::Zero();
   constexpr Frequency kFrequencyPlusInf = Frequency::PlusInfinity();
   constexpr Frequency kFrequencyMinusInf = Frequency::MinusInfinity();
+  static_assert(Frequency() == kFrequencyZero);
   static_assert(kFrequencyZero.IsZero(), "");
   static_assert(kFrequencyPlusInf.IsPlusInfinity(), "");
   static_assert(kFrequencyMinusInf.IsMinusInfinity(), "");

api/units/time_delta.h

@@ -51,7 +51,7 @@ class TimeDelta final : public rtc_units_impl::RelativeUnit<TimeDelta> {
     return FromValue(value);
   }
 
-  TimeDelta() = delete;
+  constexpr TimeDelta() = default;
 
   template <typename Sink>
   friend void AbslStringify(Sink& sink, TimeDelta value);

api/units/time_delta_unittest.cc

@@ -23,6 +23,7 @@ TEST(TimeDeltaTest, ConstExpr) {
   constexpr TimeDelta kTimeDeltaZero = TimeDelta::Zero();
   constexpr TimeDelta kTimeDeltaPlusInf = TimeDelta::PlusInfinity();
   constexpr TimeDelta kTimeDeltaMinusInf = TimeDelta::MinusInfinity();
+  static_assert(TimeDelta() == kTimeDeltaZero);
   static_assert(kTimeDeltaZero.IsZero(), "");
   static_assert(kTimeDeltaPlusInf.IsPlusInfinity(), "");
   static_assert(kTimeDeltaMinusInf.IsMinusInfinity(), "");

modules/rtp_rtcp/include/rtp_rtcp_defines.h

@@ -356,16 +356,8 @@ struct StreamDataCounters {
 };
 
 class RtpSendRates {
-  template <std::size_t... Is>
-  constexpr std::array<DataRate, sizeof...(Is)> make_zero_array(
-      std::index_sequence<Is...>) {
-    return {{(static_cast<void>(Is), DataRate::Zero())...}};
-  }
-
  public:
-  RtpSendRates()
-      : send_rates_(
-            make_zero_array(std::make_index_sequence<kNumMediaTypes>())) {}
+  constexpr RtpSendRates() = default;
   RtpSendRates(const RtpSendRates& rhs) = default;
   RtpSendRates& operator=(const RtpSendRates&) = default;
 

rtc_base/units/unit_base.h

@@ -275,6 +275,7 @@ class RelativeUnit : public UnitBase<Unit_T> {
 
  protected:
   using UnitBase<Unit_T>::UnitBase;
+  constexpr RelativeUnit() : UnitBase<Unit_T>(0) {}
 };
 
 template <class Unit_T>