When using NSS, only schedule transport socket reads when the transport buffer is empty.

net/base/nss_memio.h

Index: net/base/nss_memio.h
diff --git a/net/base/nss_memio.h b/net/base/nss_memio.h
index 7d889ebcb5ec8200a22a21430d10eb3a5c11eaab..a8bbc2c7743345150b2452fa0eae0381de621239 100644
--- a/net/base/nss_memio.h
+++ b/net/base/nss_memio.h
@@ -50,6 +50,13 @@ void memio_SetPeerName(PRFileDesc *fd, const PRNetAddr *peername);
  */
 memio_Private *memio_GetSecret(PRFileDesc *fd);
 
+/* Ask memio how many bytes were requested by a higher layer if the
+ * last attempt to read data resulted in PR_WOULD_BLOCK_ERROR, due to the
+ * transport buffer being empty. If the last attempt to read data from the
+ * memio did not result in PR_WOULD_BLOCK_ERROR, returns 0.
+ */
+int memio_GetReadRequest(memio_Private *secret);
+
 /* Ask memio where to put bytes from the network, and how many it can handle.
  * Returns bytes available to write, or 0 if none available.
  * Puts current buffer position into *buf.