Find-in-page: Search text in author shadow roots by default.

This patch lets findPlainText() enter shadow roots by default. This should
make text in author shadow roots searchable by default.

BUG=244955

Review URL: https://codereview.chromium.org/100433007

git-svn-id: svn://svn.chromium.org/blink/trunk@163751 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Delete 2 redundant bindings tests: TestExtendedEvent.idl and TestEvent.idl

TestExtendedEvent.idl and TestEvent.idl are superseded by the much more
comprehensive TestInterfaceEventConstructor.idl, and do not test anything
separate, so delete.

NOTRY=true
TBR=haraken

Review URL: https://codereview.chromium.org/106183010

git-svn-id: svn://svn.chromium.org/blink/trunk@163752 bbb929c8-8fbe-4397-9dbb-9b2b20218538