Make PassOwnPtr comparison operators const.

(This change is similar to https://codereview.chromium.org/53173005.)

Without this change the following snippet compiles (even though it
is not supposed to) and can behave unexpectedly:

bool compare(const PassOwnPtr& a, const PassOwnPtr& b)
{
   return a == b; // Convert to UnspecifiedBoolType and then compare.
}

Review URL: https://codereview.chromium.org/148493013

git-svn-id: svn://svn.chromium.org/blink/trunk@166998 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Add cross-origin BindingsSecurity checks to 'EventTarget::dispatchEvent'.

BUG=342618

Review URL: https://codereview.chromium.org/150203016

git-svn-id: svn://svn.chromium.org/blink/trunk@166999 bbb929c8-8fbe-4397-9dbb-9b2b20218538