Drop unused ExceptionCode parameters from WebGL methods.

We claim that both OESVertexArrayObject::bindVertexArrayOES and
WebGLDebugShaders::getTranslatedShaderSource throw exceptions. Neither
actually uses the ExceptionCode parameter, so we should stop claiming
that they throw exceptions.

BUG=240693

Review URL: https://chromiumcodereview.appspot.com/22186002

git-svn-id: svn://svn.chromium.org/blink/trunk@155589 bbb929c8-8fbe-4397-9dbb-9b2b20218538