Refactoring OnBeforeSendProxyHeaders->OnBeforeSendHeaders

This changes the name of OnBeforeSendProxyHeaders and related methods.

This change also calls the newly named OnBeforeSendHeaders even when not
using a proxy, so consumers have been adjusted to reflect that.

BUG=

Review-Url: https://codereview.chromium.org/1999223002
Cr-Commit-Position: refs/heads/master@{#399928}
diff --git a/net/http/http_transaction_test_util.h b/net/http/http_transaction_test_util.h
index 4d78f4d..716009f 100644
--- a/net/http/http_transaction_test_util.h
+++ b/net/http/http_transaction_test_util.h
@@ -228,8 +228,8 @@
   void SetBeforeNetworkStartCallback(
       const BeforeNetworkStartCallback& callback) override;
 
-  void SetBeforeProxyHeadersSentCallback(
-      const BeforeProxyHeadersSentCallback& callback) override;
+  void SetBeforeHeadersSentCallback(
+      const BeforeHeadersSentCallback& callback) override;
 
   int ResumeNetworkStart() override;