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

net/base/upload_element_reader.h

Index: net/base/upload_element_reader.h
diff --git a/net/base/upload_element_reader.h b/net/base/upload_element_reader.h
index 2814efa33f126f62845ff2790a76fa8b5d9438e1..267df8c89d3a9013100d56b9d0c56a318959b7f1 100644
--- a/net/base/upload_element_reader.h
+++ b/net/base/upload_element_reader.h
@@ -13,6 +13,7 @@
 
 class IOBuffer;
 class UploadBytesElementReader;
+class UploadDiskCacheEntryElementReader;
 class UploadFileElementReader;
 
 // An interface to read an upload data element.
@@ -20,6 +21,11 @@
  public:
   UploadElementReader() {}
   virtual ~UploadElementReader() {}
+
+  // Returns this instance's pointer as UploadDiskCacheEntryElementReader when
+  // possible, otherwise returns nullptr.
+  virtual const UploadDiskCacheEntryElementReader*
+  AsDiskCacheEntryReaderForTests() const;
 
   // Returns this instance's pointer as UploadBytesElementReader when possible,
   // otherwise returns NULL.