Add a ScriptForbiddenScope to ContainerNode::parserAppendChild
Add a ScriptForbiddenScope to ContainerNode::parserAppendChild

We shouldn't run script for most of this function call. We also shouldn't
dispatch events so I moved more code into the block with the
NoEventDispatchAssertion.

Review URL: https://codereview.chromium.org/303043004

git-svn-id: bf5cd6ccde378db821296732a091cfbcf5285fbd@175030 bbb929c8-8fbe-4397-9dbb-9b2b20218538

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