Added comments about expected error messages.

base/metrics/persistent_memory_allocator_unittest.cc

 // Copyright 2015 The Chromium 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 "base/metrics/persistent_memory_allocator.h"
 
 #include "base/files/file.h"
 #include "base/files/file_util.h"
 #include "base/files/memory_mapped_file.h"
 #include "base/files/scoped_temp_dir.h"
@@ skipping 547 matching lines @@
       File writer(file_path, File::FLAG_CREATE | File::FLAG_WRITE);
       ASSERT_TRUE(writer.IsValid());
       writer.Write(0, (const char*)local.data(), filesize);
     }
     ASSERT_TRUE(PathExists(file_path));
 
     mmfile.reset(new MemoryMappedFile());
     mmfile->Initialize(file_path);
     EXPECT_EQ(filesize, mmfile->length());
     if (FilePersistentMemoryAllocator::IsFileAcceptable(*mmfile)) {
-      // Make sure construction doesn't crash.
+      // Make sure construction doesn't crash. It will, however, cause
+      // error messages warning about about a corrupted memory segment.
       FilePersistentMemoryAllocator allocator(std::move(mmfile), 0, "");
       // Also make sure that iteration doesn't crash.
       PersistentMemoryAllocator::Iterator iter;
       allocator.CreateIterator(&iter);
       for (;;) {
         Reference ref = allocator.GetNextIterable(&iter, 0);
         if (!ref)
           break;
         const char* data = allocator.GetAsObject<char>(ref, 0);
         uint32_t type = allocator.GetType(ref);
@@ skipping 19 matching lines @@
       File writer(file_path, File::FLAG_CREATE | File::FLAG_WRITE);
       ASSERT_TRUE(writer.IsValid());
       writer.Write(0, (const char*)garbage.get(), filesize);
     }
     ASSERT_TRUE(PathExists(file_path));
 
     mmfile.reset(new MemoryMappedFile());
     mmfile->Initialize(file_path);
     EXPECT_EQ(filesize, mmfile->length());
     if (FilePersistentMemoryAllocator::IsFileAcceptable(*mmfile)) {
-      // Just need to make sure it doesn't crash.
+      // Make sure construction doesn't crash. It will, however, cause
+      // error messages warning about about a corrupted memory segment.
       FilePersistentMemoryAllocator allocator(std::move(mmfile), 0, "");
       EXPECT_TRUE(allocator.IsCorrupt());  // Garbage data so it should be.
     } else {
       // For filesize >= minsize, the file must be acceptable. This
       // else clause (file-not-acceptable) should be reached only if
       // filesize < minsize.
       EXPECT_GT(minsize, filesize);
     }
   }
 }
 
 }  // namespace base