Oilpan: Remove manual finalization of DatabaseContext::m_openSyncDatabases.

Blink r170443 [1] fixed a bug of HeapHashMap. We don't need to clear OwnPtrs
manually.

[1] https://src.chromium.org/viewvc/chrome?view=rev&revision=170443

BUG=347902,357113

Review URL: https://codereview.chromium.org/223453002

git-svn-id: svn://svn.chromium.org/blink/trunk@170757 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Make sure that all tracks created by the WebAudio code are proprly
initialized by making sure they are reported down to the chromium code.

Review URL: https://codereview.chromium.org/218773003

git-svn-id: svn://svn.chromium.org/blink/trunk@170758 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Oilpan: Make TreeShared GarbageCollectedFinalized.

This is the smallest possible patch to move the Node and SVGElementInstance
trees into the oilpan heap. Everything is still using the TreeShared
algorithms for deletion. Therefore, no RefPtrs can be replaced with
tracing at this point. I'll work on that next.

I initially did a patch that actually got rid of TreeShared in favor
of RefCountedGarbageCollected. However, that was too big a mouthful
and I lost track. I'm therefore going back to the approach that we
used on the branch. Move it a little at a time while keeping it
working.

R=haraken@chromium.org, kouhei@chromium.org, oilpan-reviews@chromium.org, wibling@chromium.org
BUG=357163

Review URL: https://codereview.chromium.org/213143002

git-svn-id: svn://svn.chromium.org/blink/trunk@170759 bbb929c8-8fbe-4397-9dbb-9b2b20218538