Make (and verify) public/ files compile under C.

Make (and verify) public/ files compile under C.

This involves adding some missing extern "C" { } declarations,
using FPDF_ types instead of C++ types, and converting pass
by reference arguments into pointers.

Test this using fpdfview_embedertest for simplicity.

BUG=pdfium:158
R=thestig@chromium.org

Committed: https://pdfium.googlesource.com/pdfium/+/b2aa54381811383d4a86fbe7b194907c33e8dcc1

[Tom Sepez, 2015-05-12 19:22:49]

tsepez@chromium.org changed reviewers:
+ thestig@chromium.org

[Tom Sepez, 2015-05-12 19:22:51]

Lei, just because.  Thanks.

https://codereview.chromium.org/1130843003/diff/1/BUILD.gn
File BUILD.gn (right):

https://codereview.chromium.org/1130843003/diff/1/BUILD.gn#newcode882
BUILD.gn:882: "testing/c_api_test.c",
Q: you want this in the same directory as fpdfview_embeddertest.cpp? or is here
fine?

https://codereview.chromium.org/1130843003/diff/1/fpdfsdk/src/fpdfview.cpp
File fpdfsdk/src/fpdfview.cpp (right):

https://codereview.chromium.org/1130843003/diff/1/fpdfsdk/src/fpdfview.cpp#ne...
fpdfsdk/src/fpdfview.cpp:828: DLLEXPORT FPDF_DEST STDCALL
FPDF_GetNamedDest(FPDF_DOCUMENT document, int index, void* buffer, long* buflen)
Q: possibly a breaking change.

[Lei Zhang, 2015-05-12 21:43:03]

https://codereview.chromium.org/1130843003/diff/1/BUILD.gn
File BUILD.gn (right):

https://codereview.chromium.org/1130843003/diff/1/BUILD.gn#newcode882
BUILD.gn:882: "testing/c_api_test.c",
On 2015/05/12 19:22:50, Tom Sepez wrote:
> Q: you want this in the same directory as fpdfview_embeddertest.cpp? or is
here
> fine?

Slight preference for fpdfsdk/src

https://codereview.chromium.org/1130843003/diff/1/fpdfsdk/src/fpdfview.cpp
File fpdfsdk/src/fpdfview.cpp (right):

https://codereview.chromium.org/1130843003/diff/1/fpdfsdk/src/fpdfview.cpp#ne...
fpdfsdk/src/fpdfview.cpp:828: DLLEXPORT FPDF_DEST STDCALL
FPDF_GetNamedDest(FPDF_DOCUMENT document, int index, void* buffer, long* buflen)
On 2015/05/12 19:22:50, Tom Sepez wrote:
> Q: possibly a breaking change.

Ok. Shouldn't be too hard for callers to adapt.

https://codereview.chromium.org/1130843003/diff/1/testing/c_api_test.c
File testing/c_api_test.c (right):

https://codereview.chromium.org/1130843003/diff/1/testing/c_api_test.c#newcode35
testing/c_api_test.c:35: CHK(FORM_DoDocumentAAction);
Do we want to organize these by header file?

https://codereview.chromium.org/1130843003/diff/1/testing/c_api_test.h
File testing/c_api_test.h (right):

https://codereview.chromium.org/1130843003/diff/1/testing/c_api_test.h#newcode1
testing/c_api_test.h:1: // Copyright (c) 2015 PDFium Authors. All rights
reserved.
nit: no (c)

[Tom Sepez, 2015-05-12 22:36:56]

https://codereview.chromium.org/1130843003/diff/1/BUILD.gn
File BUILD.gn (right):

https://codereview.chromium.org/1130843003/diff/1/BUILD.gn#newcode882
BUILD.gn:882: "testing/c_api_test.c",
On 2015/05/12 21:43:03, Lei Zhang wrote:
> On 2015/05/12 19:22:50, Tom Sepez wrote:
> > Q: you want this in the same directory as fpdfview_embeddertest.cpp? or is
> here
> > fine?
> 
> Slight preference for fpdfsdk/src

Done.

https://codereview.chromium.org/1130843003/diff/1/fpdfsdk/src/fpdfview.cpp
File fpdfsdk/src/fpdfview.cpp (right):

https://codereview.chromium.org/1130843003/diff/1/fpdfsdk/src/fpdfview.cpp#ne...
fpdfsdk/src/fpdfview.cpp:828: DLLEXPORT FPDF_DEST STDCALL
FPDF_GetNamedDest(FPDF_DOCUMENT document, int index, void* buffer, long* buflen)
On 2015/05/12 21:43:03, Lei Zhang wrote:
> On 2015/05/12 19:22:50, Tom Sepez wrote:
> > Q: possibly a breaking change.
> 
> Ok. Shouldn't be too hard for callers to adapt.

Done.

https://codereview.chromium.org/1130843003/diff/1/testing/c_api_test.c
File testing/c_api_test.c (right):

https://codereview.chromium.org/1130843003/diff/1/testing/c_api_test.c#newcode35
testing/c_api_test.c:35: CHK(FORM_DoDocumentAAction);
On 2015/05/12 21:43:03, Lei Zhang wrote:
> Do we want to organize these by header file?

Yeah.  I went and just sorted the lot of them, but seems to make thing worse. 
By order of appearance in headers, I guess.

https://codereview.chromium.org/1130843003/diff/1/testing/c_api_test.h
File testing/c_api_test.h (right):

https://codereview.chromium.org/1130843003/diff/1/testing/c_api_test.h#newcode1
testing/c_api_test.h:1: // Copyright (c) 2015 PDFium Authors. All rights
reserved.
On 2015/05/12 21:43:03, Lei Zhang wrote:
> nit: no (c)

Done.

[Lei Zhang, 2015-05-12 23:06:04]

lgtm

There's a couple more typos in the commit msg.

[Tom Sepez, 2015-05-12 23:17:08]

Committed patchset #3 (id:40001) manually as
b2aa54381811383d4a86fbe7b194907c33e8dcc1 (presubmit successful).