Revert "Oilpan: Replace the positive heap-contains cache with a binary search tree of memory regions."

This reverts commit e38be3fb251cd7852f8c0a0777f1739922363390.

These content_unittests were crashing after blink r227397

WebIDBCursorImplTest.PrefetchTest
WebIDBCursorImplTest.AdvancePrefetchTest

BUG=420086
TBR=zerny@chromium.org

Review URL: https://codereview.chromium.org/626903002

git-svn-id: svn://svn.chromium.org/blink/trunk@183200 bbb929c8-8fbe-4397-9dbb-9b2b20218538