Fix layering violation in CPDF_Document::FromFPDFDocument().

Fix layering violation in CPDF_Document::FromFPDFDocument().

Make this a function in the fpdfsdk/ layer, rather than a method
in the core/ layer. Nothing in core should know about public FPDF
types.

BUG=pdfium:217
R=thestig@chromium.org

Committed: https://pdfium.googlesource.com/pdfium/+/86adb658843658969041a13bf6cf0cc950ffe8ed

[Tom Sepez, 2015-10-15 17:36:06]

tsepez@chromium.org changed reviewers:
+ jun_fang@foxitsoftware.com, thestig@chromium.org

[Tom Sepez, 2015-10-15 17:36:56]

Lei, for review. Jun, FYI following your layering guidelines.

[Tom Sepez, 2015-10-15 17:45:56]

https://codereview.chromium.org/1396283006/diff/1/fpdfsdk/include/fsdk_define.h
File fpdfsdk/include/fsdk_define.h (right):

https://codereview.chromium.org/1396283006/diff/1/fpdfsdk/include/fsdk_define...
fpdfsdk/include/fsdk_define.h:60: CPDF_Document*
CPDFDocumentFromFPDFDocument(FPDF_DOCUMENT doc);
Should this be an inline? Its just a cast or a ptr deref and cast under XFA?

[Tom Sepez, 2015-10-15 17:47:56]

On 2015/10/15 17:45:56, Tom Sepez wrote:
>
https://codereview.chromium.org/1396283006/diff/1/fpdfsdk/include/fsdk_define.h
> File fpdfsdk/include/fsdk_define.h (right):
> 
>
https://codereview.chromium.org/1396283006/diff/1/fpdfsdk/include/fsdk_define...
> fpdfsdk/include/fsdk_define.h:60: CPDF_Document*
> CPDFDocumentFromFPDFDocument(FPDF_DOCUMENT doc);
> Should this be an inline? Its just a cast or a ptr deref and cast under XFA?
Alternatively, keeping it in .cpp file prevents dragging xfa headers through
everything.

[Lei Zhang, 2015-10-15 21:50:24]

lgtm

https://codereview.chromium.org/1396283006/diff/1/fpdfsdk/include/fsdk_define.h
File fpdfsdk/include/fsdk_define.h (right):

https://codereview.chromium.org/1396283006/diff/1/fpdfsdk/include/fsdk_define...
fpdfsdk/include/fsdk_define.h:60: CPDF_Document*
CPDFDocumentFromFPDFDocument(FPDF_DOCUMENT doc);
On 2015/10/15 17:45:56, Tom Sepez wrote:
> Should this be an inline? Its just a cast or a ptr deref and cast under XFA?

Will it actually make a measurable difference? Up to you.

[Tom Sepez, 2015-10-15 21:51:47]

Committed patchset #1 (id:1) manually as
86adb658843658969041a13bf6cf0cc950ffe8ed (presubmit successful).