Store the address of the page data map's value for proper referencing.

CPDF_Pattern objects are counted and maintained in m_PatternedMap.
When a CPDF_Pattern object "pattern" is deleted, it's address is marked as NULL in m_PatternMap.
This patch stores the address of CPDF_Pattern's adderss in all objects that references "pattern",
to ensure valid referencing after deletion.

BUG=416319, 419976, 418392
R=tsepez@chromium.org

Review URL: https://codereview.chromium.org/656753002