Remove <assert.h> includes from PDFium

The code now uses DCHECK(), and third_party/base/check.h is
capable of pulling in whatever it needs only in the places
that actually need it.

Change-Id: Ibd23bb0ace36f430736845e6c870469648f41020
Reviewed-on: https://pdfium-review.googlesource.com/c/pdfium/+/79771
Reviewed-by: Lei Zhang <thestig@chromium.org>
Commit-Queue: Tom Sepez <tsepez@chromium.org>
diff --git a/core/fpdfapi/parser/cpdf_syntax_parser.cpp b/core/fpdfapi/parser/cpdf_syntax_parser.cpp
index 0c22fbe..889088b 100644
--- a/core/fpdfapi/parser/cpdf_syntax_parser.cpp
+++ b/core/fpdfapi/parser/cpdf_syntax_parser.cpp
@@ -411,7 +411,7 @@
 };
 
 void CPDF_SyntaxParser::RecordingToNextWord() {
-  assert(m_TrailerEnds);
+  DCHECK(m_TrailerEnds);
 
   EofState eof_state = EofState::kInitial;
   // Find the first character which is neither whitespace, nor part of a
diff --git a/core/fxcrt/fx_system.h b/core/fxcrt/fx_system.h
index 1f01817..c77bc99 100644
--- a/core/fxcrt/fx_system.h
+++ b/core/fxcrt/fx_system.h
@@ -7,7 +7,6 @@
 #ifndef CORE_FXCRT_FX_SYSTEM_H_
 #define CORE_FXCRT_FX_SYSTEM_H_
 
-#include <assert.h>
 #include <math.h>
 #include <stdarg.h>
 #include <stddef.h>
diff --git a/testing/image_diff/image_diff.cpp b/testing/image_diff/image_diff.cpp
index 5bfef4c..4afbc77 100644
--- a/testing/image_diff/image_diff.cpp
+++ b/testing/image_diff/image_diff.cpp
@@ -8,7 +8,6 @@
 // The exact format of this tool's output to stdout is important, to match
 // what the run-webkit-tests script expects.
 
-#include <assert.h>
 #include <stdint.h>
 #include <stdio.h>
 #include <string.h>