Oilpan: Remove guardRef and guardDeref from TreeScope.

This leads to a situation where Nodes and their TreeScope can die
at the same time and Nodes can no longer touch their document in
their destructors.

Instead we now have the following property:

A Node is either explicitly removed from its container and
|removedFrom| is called at that point, or the Node and the
TreeScope die at the same time.

This allows us to remove code from destructors that is only
there to clean up the TreeScope if the object was not
explicitly removed from the TreeScope. Other code in destructors
that go through the TreeScope to carry something out is
replaced by weak processing instead.

BUG=357163

Review URL: https://codereview.chromium.org/235113002

git-svn-id: svn://svn.chromium.org/blink/trunk@172746 bbb929c8-8fbe-4397-9dbb-9b2b20218538
TimelinePanel: convert 'data' property getter into function in TimelineModel.Record

Drive by fix: replace argument name 'record' with 'timelineEvent' for better readability.

BUG=361045

Review URL: https://codereview.chromium.org/254983004

git-svn-id: svn://svn.chromium.org/blink/trunk@172747 bbb929c8-8fbe-4397-9dbb-9b2b20218538