Remove unnecessary static_cast<SocketStreamHandle*>().
Remove unnecessary static_cast<SocketStreamHandle*>().

|this| is SocketStreamHandle*. These static_casts are unnecessary.

BUG=

Review URL: https://codereview.chromium.org/105513004

git-svn-id: bf5cd6ccde378db821296732a091cfbcf5285fbd@163501 bbb929c8-8fbe-4397-9dbb-9b2b20218538

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