AU: Push seeks in http fetching to the progress percentage.

mock_http_fetcher.h

Index: mock_http_fetcher.h
diff --git a/mock_http_fetcher.h b/mock_http_fetcher.h
index 91d50dd8747c0bdb85280f195fb59fd10e4ff4f7..f0830f0c553ee7b670c055e94159d9d1b5495cda 100644
--- a/mock_http_fetcher.h
+++ b/mock_http_fetcher.h
@@ -35,7 +35,11 @@ class MockHttpFetcher : public HttpFetcher {
   ~MockHttpFetcher();
 
   // Ignores this.
-  virtual void SetOffset(off_t offset) {}
+  virtual void SetOffset(off_t offset) {
+    sent_size_ = offset;
+    if (delegate_)
+      delegate_->SeekToOffset(offset);
+  }
 
   // Begins the transfer if it hasn't already begun.
   virtual void BeginTransfer(const std::string& url);