Introduce dchecked_cast, and start using it

It's the faster, less strict cousin of checked_cast.

BUG=none

Review-Url: https://codereview.webrtc.org/2714063002
Cr-Commit-Position: refs/heads/master@{#16958}
diff --git a/webrtc/modules/audio_coding/neteq/neteq_impl.cc b/webrtc/modules/audio_coding/neteq/neteq_impl.cc
index 09a3296..786cb84 100644
--- a/webrtc/modules/audio_coding/neteq/neteq_impl.cc
+++ b/webrtc/modules/audio_coding/neteq/neteq_impl.cc
@@ -199,7 +199,7 @@
   }
   RTC_DCHECK_EQ(
       audio_frame->sample_rate_hz_,
-      rtc::checked_cast<int>(audio_frame->samples_per_channel_ * 100));
+      rtc::dchecked_cast<int>(audio_frame->samples_per_channel_ * 100));
   SetAudioFrameActivityAndType(vad_->enabled(), LastOutputType(),
                                last_vad_activity_, audio_frame);
   last_vad_activity_ = audio_frame->vad_activity_;
@@ -826,7 +826,7 @@
       if (packet_length_samples != decision_logic_->packet_length_samples()) {
         decision_logic_->set_packet_length_samples(packet_length_samples);
         delay_manager_->SetPacketAudioLength(
-            rtc::checked_cast<int>((1000 * packet_length_samples) / fs_hz_));
+            rtc::dchecked_cast<int>((1000 * packet_length_samples) / fs_hz_));
       }
     }
 
@@ -1131,7 +1131,7 @@
       last_mode_ == kModePreemptiveExpandLowEnergy) {
     // Subtract (samples_left + output_size_samples_) from sampleMemory.
     decision_logic_->AddSampleMemory(
-        -(samples_left + rtc::checked_cast<int>(output_size_samples_)));
+        -(samples_left + rtc::dchecked_cast<int>(output_size_samples_)));
   }
 
   // Check if it is time to play a DTMF event.
@@ -1157,11 +1157,9 @@
   // Check if we already have enough samples in the |sync_buffer_|. If so,
   // change decision to normal, unless the decision was merge, accelerate, or
   // preemptive expand.
-  if (samples_left >= rtc::checked_cast<int>(output_size_samples_) &&
-      *operation != kMerge &&
-      *operation != kAccelerate &&
-      *operation != kFastAccelerate &&
-      *operation != kPreemptiveExpand) {
+  if (samples_left >= rtc::dchecked_cast<int>(output_size_samples_) &&
+      *operation != kMerge && *operation != kAccelerate &&
+      *operation != kFastAccelerate && *operation != kPreemptiveExpand) {
     *operation = kNormal;
     return 0;
   }
@@ -1454,7 +1452,7 @@
     return 0;
   }
 
-  while (*decoded_length < rtc::checked_cast<int>(output_size_samples_)) {
+  while (*decoded_length < rtc::dchecked_cast<int>(output_size_samples_)) {
     const int length = decoder->Decode(
             nullptr, 0, fs_hz_,
             (decoded_buffer_length_ - *decoded_length) * sizeof(int16_t),
@@ -1500,7 +1498,7 @@
       const auto& result = *opt_result;
       *speech_type = result.speech_type;
       if (result.num_decoded_samples > 0) {
-        *decoded_length += rtc::checked_cast<int>(result.num_decoded_samples);
+        *decoded_length += rtc::dchecked_cast<int>(result.num_decoded_samples);
         // Update |decoder_frame_length_| with number of samples per channel.
         decoder_frame_length_ =
             result.num_decoded_samples / decoder->Channels();
@@ -1513,7 +1511,7 @@
       packet_list->clear();
       break;
     }
-    if (*decoded_length > rtc::checked_cast<int>(decoded_buffer_length_)) {
+    if (*decoded_length > rtc::dchecked_cast<int>(decoded_buffer_length_)) {
       // Guard against overflow.
       LOG(LS_WARNING) << "Decoded too much.";
       packet_list->clear();
@@ -1986,7 +1984,8 @@
       packet_duration = packet->frame->Duration();
       // TODO(ossu): Is this the correct way to track Opus FEC packets?
       if (packet->priority.codec_level > 0) {
-        stats_.SecondaryDecodedSamples(rtc::checked_cast<int>(packet_duration));
+        stats_.SecondaryDecodedSamples(
+            rtc::dchecked_cast<int>(packet_duration));
       }
     } else if (!has_cng_packet) {
       LOG(LS_WARNING) << "Unknown payload type "
@@ -2029,7 +2028,7 @@
     packet_buffer_->DiscardAllOldPackets(timestamp_);
   }
 
-  return rtc::checked_cast<int>(extracted_samples);
+  return rtc::dchecked_cast<int>(extracted_samples);
 }
 
 void NetEqImpl::UpdatePlcComponents(int fs_hz, size_t channels) {