Add [c]begin() and [c]end() member functions to rtc::Buffer

webrtc/base/buffer.h

Index: webrtc/base/buffer.h
diff --git a/webrtc/base/buffer.h b/webrtc/base/buffer.h
index 44f941eb60b2bb1016874d6f94bbda52a759f10a..85e6efb74e432f8229d43532671198eeccc2adcd 100644
--- a/webrtc/base/buffer.h
+++ b/webrtc/base/buffer.h
@@ -179,6 +179,13 @@ class BufferT {
     return data()[index];
   }
 
+  T* begin() { return data(); }
+  T* end() { return data() + size(); }
+  const T* begin() const { return data(); }
+  const T* end() const { return data() + size(); }
+  const T* cbegin() const { return data(); }
+  const T* cend() const { return data() + size(); }
+
   // The SetData functions replace the contents of the buffer. They accept the
   // same input types as the constructors.
   template <typename U,