On Document disposal, only dispose of script runner.
Reinstate the invariant that a Document always has a ScriptRunner
(m_scriptRunner), even after the document has been dispose()d.
The reason for disposing the Document's ScriptRunner is to clear
out back references that would otherwise cause the Document to
leak. Do just that, but don't destruct the now-empty ScriptRunner
object.
R=haraken
BUG=536796
Review URL: https://codereview.chromium.org/1380543002
Cr-Commit-Position: refs/heads/master@{#351385}
5 files changed
