Add code style check error for using static_cast instead of toFoo function.

We are migrating to new syntax of calling toFoo for any type of static_cast we do on Foo objects. We are adding to more and more classes toFoo helper functions, so we should ensure that the added helpers are actually *used* in the code. Currently, there is no enforcement on the same and through this change we are adding that style check which will fail any patch upload if we are not following toFoo style (if toFoo exists). As part of testing,  executed check-webkit-style on all source files which still have static_cast<Foo*> code syntax. The script throws style error if we are using static_cast though we already have toFoo helper function. If toFoo is not yet defined, it doesn't throw any error right now (should that be changed?) 

BUG=None

TEST=none; no behavior change;

Review URL: https://chromiumcodereview.appspot.com/23654034

git-svn-id: svn://svn.chromium.org/blink/trunk@158059 bbb929c8-8fbe-4397-9dbb-9b2b20218538