Make m_pShadingObj a CPDF_Stream instead of CPDF_Object.

Make m_pShadingObj a CPDF_Stream instead of CPDF_Object.

This object is required to be a stream and was being converted as such. With
the new type checking this caused us to pass a nullptr where previously we'd
have, incorrectly, cast a CPDF_Dictionary to a CPDF_Stream.

This CL changes the m_pShadingObj to always be a CPDF_Stream. Then, we never
go down the bad code path because we check if m_pShadingObj is nullptr earlier
and bail out.

BUG=chromium:547706
R=tsepez@chromium.org

Committed: https://pdfium.googlesource.com/pdfium/+/85361b227ad6786d2aeef8409b79a8d077a26ee9

[dsinclair, 2015-10-26 19:58:02]

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

[dsinclair, 2015-10-26 19:58:02]

PTAL.

https://codereview.chromium.org/1426713002/diff/1/core/src/fpdfapi/fpdf_page/...
File core/src/fpdfapi/fpdf_page/fpdf_page_pattern.cpp (right):

https://codereview.chromium.org/1426713002/diff/1/core/src/fpdfapi/fpdf_page/...
core/src/fpdfapi/fpdf_page/fpdf_page_pattern.cpp:112: if (pShadingDict == NULL)
{
We bail out here and fail to Load the shading pattern because m_pShadingObj will
now be a nullptr if it isn't a stream.

[Tom Sepez, 2015-10-26 20:02:36]

LGTM % nit

https://codereview.chromium.org/1426713002/diff/1/core/src/fpdfapi/fpdf_rende...
File core/src/fpdfapi/fpdf_render/fpdf_render_pattern_embeddertest.cpp (right):

https://codereview.chromium.org/1426713002/diff/1/core/src/fpdfapi/fpdf_rende...
core/src/fpdfapi/fpdf_render/fpdf_render_pattern_embeddertest.cpp:11: // Test
trailer dictionary with $$ze instead of Size.
nit: fix this comment.

[dsinclair, 2015-10-26 20:12:32]

https://codereview.chromium.org/1426713002/diff/1/core/src/fpdfapi/fpdf_rende...
File core/src/fpdfapi/fpdf_render/fpdf_render_pattern_embeddertest.cpp (right):

https://codereview.chromium.org/1426713002/diff/1/core/src/fpdfapi/fpdf_rende...
core/src/fpdfapi/fpdf_render/fpdf_render_pattern_embeddertest.cpp:11: // Test
trailer dictionary with $$ze instead of Size.
On 2015/10/26 20:02:36, Tom Sepez wrote:
> nit: fix this comment.

Done.

[dsinclair, 2015-10-26 20:14:26]

Committed patchset #2 (id:20001) manually as
85361b227ad6786d2aeef8409b79a8d077a26ee9 (presubmit successful).