Fix extraction of colour components in CPDF_DIBSource::DownSampleScanline32Bit

core/src/fpdfapi/fpdf_render/fpdf_render_loadimage_embeddertest.cpp

 // Copyright 2015 PDFium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "testing/embedder_test.h"
 #include "testing/gtest/include/gtest/gtest.h"
 
-class FPDFPageFuncEmbeddertest : public EmbedderTest {};
+class FPDFRenderLoadImageEmbeddertest : public EmbedderTest {};
 
-TEST_F(FPDFPageFuncEmbeddertest, Bug_551460) {
-  // Should not crash under ASan.
-  // Tests that the number of inputs is not simply calculated from the domain
-  // and trusted. The number of inputs has to be 1.
-  EXPECT_TRUE(OpenDocument("bug_551460.pdf"));
+TEST_F(FPDFRenderLoadImageEmbeddertest, Bug_554151) {
+  // Test scanline downsampling with a BitsPerComponent of 4.
+  // Should not crash.
+  EXPECT_TRUE(OpenDocument("bug_554151.pdf"));
   FPDF_PAGE page = LoadPage(0);
   EXPECT_NE(nullptr, page);
   FPDF_BITMAP bitmap = RenderPage(page);
   FPDFBitmap_Destroy(bitmap);
   UnloadPage(page);
 }