Introduce dchecked_cast, and start using it

webrtc/base/safe_conversions.h

Index: webrtc/base/safe_conversions.h
diff --git a/webrtc/base/safe_conversions.h b/webrtc/base/safe_conversions.h
index 51239bc65dd33ceec4bf68ce7ce8d662dbaa13c9..ff9cc44bc2c183ecb831acdc01fbc2ef1e7f4d66 100644
--- a/webrtc/base/safe_conversions.h
+++ b/webrtc/base/safe_conversions.h
@@ -27,14 +27,20 @@ inline bool IsValueInRangeForNumericType(Src value) {
   return internal::RangeCheck<Dst>(value) == internal::TYPE_VALID;
 }
 
-// checked_cast<> is analogous to static_cast<> for numeric types,
-// except that it CHECKs that the specified numeric conversion will not
-// overflow or underflow. NaN source will always trigger a CHECK.
+// checked_cast<> and dchecked_cast<> are analogous to static_cast<> for
+// numeric types, except that they [D]CHECK that the specified numeric
+// conversion will not overflow or underflow. NaN source will always trigger
+// the [D]CHECK.
 template <typename Dst, typename Src>
 inline Dst checked_cast(Src value) {
   RTC_CHECK(IsValueInRangeForNumericType<Dst>(value));
   return static_cast<Dst>(value);
 }
+template <typename Dst, typename Src>
+inline Dst dchecked_cast(Src value) {
+  RTC_DCHECK(IsValueInRangeForNumericType<Dst>(value));
+  return static_cast<Dst>(value);
+}
 
 // saturated_cast<> is analogous to static_cast<> for numeric types, except
 // that the specified numeric conversion will saturate rather than overflow or