Revert of [Blob] BlobReader class & tests, and removal of all redundant reading.

net/base/upload_element_reader.cc

Index: net/base/upload_element_reader.cc
diff --git a/net/base/upload_element_reader.cc b/net/base/upload_element_reader.cc
index 2a95eb816aec97f64924c265879cb67bb53e11c0..70b657cf868bf9dec74c4d342f218bf12a3929a2 100644
--- a/net/base/upload_element_reader.cc
+++ b/net/base/upload_element_reader.cc
@@ -5,6 +5,11 @@
 #include "net/base/upload_element_reader.h"
 
 namespace net {
+
+const UploadDiskCacheEntryElementReader*
+UploadElementReader::AsDiskCacheEntryReaderForTests() const {
+  return nullptr;
+}
 
 const UploadBytesElementReader* UploadElementReader::AsBytesReader() const {
   return nullptr;