Merge to XFA: Add type cast definitions for CPDF_Array.

Merge to XFA: Add type cast definitions for CPDF_Array.

This Cl adds ToArray, CPDF_Object::AsArray and CPDF_Object::IsArray and
updates the src to use them as needed.

BUG=pdfium:201
R=thestig@chromium.org, tsepez@chromium.org

Review URL: https://codereview.chromium.org/1417893003 .

(cherry picked from commit c2bfc000e502c42c9a3017038fd9104c7997d126)

Committed: https://pdfium.googlesource.com/pdfium/+/2b11dc1220746d2f6f97a940fc9e4235c8ed4975

[dsinclair, 2015-10-22 13:39:29]

PTAL. Merge conflict marked.

https://codereview.chromium.org/1419643005/diff/1/fpdfsdk/src/fsdk_actionhand...
File fpdfsdk/src/fsdk_actionhandler.cpp (right):

https://codereview.chromium.org/1419643005/diff/1/fpdfsdk/src/fsdk_actionhand...
fpdfsdk/src/fsdk_actionhandler.cpp:437: CPDF_Document* pPDFDocument =
pDocument->GetDocument()->GetPDFDoc();
Merge conflict:

master branch: pDocument->GetDocument();
XFA branch   : pDocument->GetDocument()->GetPDFDoc();

[Lei Zhang, 2015-10-22 18:54:24]

lgtm

I think tsepez has plans to abstract away that conflict.

[Tom Sepez, 2015-10-22 18:59:24]

lgtm

[dsinclair, 2015-10-22 19:02:09]

Committed patchset #1 (id:1) manually as
2b11dc1220746d2f6f97a940fc9e4235c8ed4975 (presubmit successful).