Add transparent Contains() test to unowned_ptr_unittest.cpp

Show that pdfium::Contains() can be applied as expected, as this
eventually translates into a call to find() with a transparent
comparison.

Change-Id: I4ef6d1ec1cc5f675fb3c6ad51323b2c6cecdd749
Reviewed-on: https://pdfium-review.googlesource.com/c/pdfium/+/98392
Auto-Submit: Tom Sepez <tsepez@chromium.org>
Commit-Queue: Lei Zhang <thestig@chromium.org>
Commit-Queue: Tom Sepez <tsepez@chromium.org>
Reviewed-by: Lei Zhang <thestig@chromium.org>

core/fxcrt/unowned_ptr_unittest.cpp

diff --git a/core/fxcrt/unowned_ptr_unittest.cpp b/core/fxcrt/unowned_ptr_unittest.cpp
index 92cf294..7862e5e 100644
--- a/core/fxcrt/unowned_ptr_unittest.cpp
+++ b/core/fxcrt/unowned_ptr_unittest.cpp
@@ -10,6 +10,7 @@
 #include <utility>
 
 #include "testing/gtest/include/gtest/gtest.h"
+#include "third_party/base/containers/contains.h"
 
 namespace fxcrt {
 namespace {
@@ -203,6 +204,8 @@
   holder.insert(ptr1);
   EXPECT_NE(holder.end(), holder.find(&foos[0]));
   EXPECT_EQ(holder.end(), holder.find(&foos[1]));
+  EXPECT_TRUE(pdfium::Contains(holder, &foos[0]));
+  EXPECT_FALSE(pdfium::Contains(holder, &foos[1]));
 }
 
 }  // namespace fxcrt