Add stack direction heap unit test.

Source/platform/heap/HeapTest.cpp

 /*
  * Copyright (C) 2013 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 5520 matching lines @@
     // of the old buffer to both ends of the expanded buffer, along with
     // re-adjusting both start&end indices in terms of that expanded buffer.
     EXPECT_EQ(80u, deque->size());
     i = 0;
     for (const auto& intWrapper : *deque) {
         EXPECT_EQ(i + 50, intWrapper->value());
         i++;
     }
 }
 
+namespace {
+
+enum GrowthDirection {
+    GrowsTowardsHigher,
+    GrowsTowardsLower,
+};
+
+NEVER_INLINE NO_SANITIZE_ADDRESS GrowthDirection stackGrowthDirection()
+{
+    // Disable ASan, otherwise its stack checking (use-after-return) will
+    // confuse the direction check.
+    static char* previous = nullptr;
+    char dummy;
+    if (!previous) {
+        previous = &dummy;
+        GrowthDirection result = stackGrowthDirection();
+        previous = nullptr;
+        return result;
+    }
+    ASSERT(&dummy != previous);
+    return &dummy < previous ? GrowsTowardsLower : GrowsTowardsHigher;
+}
+
+} // namespace
+
+TEST(HeapTest, StackGrowthDirection)
+{
+    // The implementation of marking probes stack usage as it runs,
+    // and has a builtin assumption that the stack grows towards
+    // lower addresses.
+    EXPECT_EQ(GrowsTowardsLower, stackGrowthDirection());
+}
+
 } // namespace blink