net: Move the logic reading upload elements to UploadData::Element.

net/base/upload_data.h

Index: net/base/upload_data.h
diff --git a/net/base/upload_data.h b/net/base/upload_data.h
index d42ffad16352f8e7be97fc08f0b8f8440af87d44..a7f3d34da61e2d17bd3ce8a8928a15ef44171dc9 100644
--- a/net/base/upload_data.h
+++ b/net/base/upload_data.h
@@ -110,13 +110,31 @@ class NET_EXPORT UploadData : public base::RefCounted<UploadData> {
     // is returned.  This is done for consistency with Mozilla.
     uint64 GetContentLength();
 
-    // Returns a FileStream opened for reading for this element, positioned at
-    // |file_range_offset_|.  The caller gets ownership and is responsible
-    // for cleaning up the FileStream. Returns NULL if this element is not of
-    // type TYPE_FILE or if the file is not openable.
-    FileStream* NewFileStreamForReading();
+    // Reads up to |buf_len| bytes synchronously. Returns the number of bytes
+    // read. This function never fails. If there's less data to read than we
+    // initially observed, then pad with zero (this can happen with files).
+    // |buf_len| must be greater than 0.
+    int ReadSync(char* buf, int buf_len);
+
+    // Returns the number of bytes remaining to read.
+    uint64 BytesRemaining();
+
+    // Resets the offset to zero, so that the element can be reread.
+    void ResetOffset() { offset_ = 0; }
 
    private:
+    // Returns a FileStream opened for reading for this element, positioned
+    // at |file_range_offset_|. Returns NULL if the file is not openable.
+    FileStream* OpenFileStream();
+
+    // Reads up to |buf_len| bytes synchronously from memory (i.e. type_ is
+    // TYPE_BYTES or TYPE_CHUNK).
+    int ReadFromMemorySync(char* buf, int buf_len);
+
+    // Reads up to |buf_len| bytes synchronously from a file (i.e. type_ is
+    // TYPE_FILE).
+    int ReadFromFileSync(char* buf, int buf_len);
+
     // Allows tests to override the result of GetContentLength.
     void SetContentLength(uint64 content_length) {
       override_content_length_ = true;
@@ -134,6 +152,12 @@ class NET_EXPORT UploadData : public base::RefCounted<UploadData> {
     bool override_content_length_;
     bool content_length_computed_;
     uint64 content_length_;
+
+    // The byte offset from the beginning of the element data. Used to track
+    // the current position when reading data.
+    size_t offset_;
+
+    // The stream of the element data, if this element is of TYPE_FILE.
     FileStream* file_stream_;
 
     FRIEND_TEST_ALL_PREFIXES(UploadDataStreamTest, FileSmallerThanLength);
@@ -180,6 +204,11 @@ class NET_EXPORT UploadData : public base::RefCounted<UploadData> {
   // upload data is not chunked, and all elemnts are of TYPE_BYTES).
   bool IsInMemory() const;
 
+  // Resets the offset of each upload data element to zero, so that the
+  // upload data can be reread. This can happen if the same upload data is
+  // reused for a new UploadDataStream.
+  void ResetOffset();
+
   std::vector<Element>* elements() {
     return &elements_;
   }