Update language to comply with Android's inclusive language guidance

More details in: https://source.android.com/setup/contribute/respectful-code

Bug: 161896447
Test: build, run unittests
Change-Id: I6a7136b01ecce948a3997c60b7dcec848331e8ef
diff --git a/common/mock_http_fetcher.h b/common/mock_http_fetcher.h
index 0f04319..dec81b0 100644
--- a/common/mock_http_fetcher.h
+++ b/common/mock_http_fetcher.h
@@ -76,7 +76,7 @@
   void set_connect_timeout(int connect_timeout_seconds) override {}
   void set_max_retry_count(int max_retry_count) override {}
 
-  // Dummy: no bytes were downloaded.
+  // No bytes were downloaded in the mock class.
   size_t GetBytesDownloaded() override { return sent_size_; }
 
   // Begins the transfer if it hasn't already begun.