The root cause of this issue is shown as below:
Patterns are managed in CPDF_DocPageData. When
a document is closed, all patterns will be
released in the deconstruction of CPDF_DocPageData.
However, some patterns which are referenced in
CPDF_Color can't get the notification from the
destroy of CPDF_DocPageData. It will cause
use-after-free in CPDF_Color::~CPDF_Color.

BUG=392719
R=tsepez@chromium.org

Review URL: https://codereview.chromium.org/439693002