APIs and tests for extracting bitmaps from image objects

Added FPDFImageObj_GetBitmap() that returns the bitmap of an image
object, and a FPDFBitmap_GetFormat() that returns the format of a
bitmap.
    * Fixed a small bitmap conversion bug in cfx_dibsource.cpp.
    * Enabled EmbedderTest::CompareBitmap() to support different formats
      of bitmaps.
    * Added an embedder test and a test PDF file with images of many
      different formats.

Bug=pdfium:677

Change-Id: I6a72f9d969cf5f3577db9400ca33197c213622ed
Reviewed-on: https://pdfium-review.googlesource.com/9690
Reviewed-by: Lei Zhang <thestig@chromium.org>
Commit-Queue: Jane Liu <janeliulwq@google.com>
diff --git a/fpdfsdk/fpdfview_c_api_test.c b/fpdfsdk/fpdfview_c_api_test.c
index 7d42be8..e47f4d1 100644
--- a/fpdfsdk/fpdfview_c_api_test.c
+++ b/fpdfsdk/fpdfview_c_api_test.c
@@ -132,6 +132,7 @@
     CHK(FPDFImageObj_LoadJpegFileInline);
     CHK(FPDFImageObj_SetMatrix);
     CHK(FPDFImageObj_SetBitmap);
+    CHK(FPDFImageObj_GetBitmap);
     CHK(FPDFPageObj_CreateNewPath);
     CHK(FPDFPageObj_CreateNewRect);
     CHK(FPDFPath_SetStrokeColor);
@@ -302,6 +303,7 @@
     CHK(FPDF_PageToDevice);
     CHK(FPDFBitmap_Create);
     CHK(FPDFBitmap_CreateEx);
+    CHK(FPDFBitmap_GetFormat);
     CHK(FPDFBitmap_FillRect);
     CHK(FPDFBitmap_GetBuffer);
     CHK(FPDFBitmap_GetWidth);