Move ArrayView, Buffer and related to webrtc namespace

Bug: webrtc:42232595
Change-Id: Idcd603d534eda6a5c1eea36d2c1c1e80c19fa0ca
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/376561
Reviewed-by: Tomas Gunnarsson <tommi@webrtc.org>
Reviewed-by: Mirko Bonadei <mbonadei@webrtc.org>
Commit-Queue: Evan Shrubsole <eshr@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#43863}
diff --git a/rtc_base/zero_memory.h b/rtc_base/zero_memory.h
index b92f52f..c5cd2d5 100644
--- a/rtc_base/zero_memory.h
+++ b/rtc_base/zero_memory.h
@@ -17,7 +17,7 @@
 
 #include "api/array_view.h"
 
-namespace rtc {
+namespace webrtc {
 
 // Fill memory with zeros in a way that the compiler doesn't optimize it away
 // even if the pointer is not used afterwards.
@@ -30,6 +30,12 @@
   ExplicitZeroMemory(a.data(), a.size());
 }
 
+}  //  namespace webrtc
+
+// Re-export symbols from the webrtc namespace for backwards compatibility.
+// TODO(bugs.webrtc.org/4222596): Remove once all references are updated.
+namespace rtc {
+using ::webrtc::ExplicitZeroMemory;
 }  // namespace rtc
 
 #endif  // RTC_BASE_ZERO_MEMORY_H_