Simplify DefaultAllocator::Quantizer using partitionAllocActualSize()

Source/platform/PurgeableVectorTest.cpp

 /*
  * Copyright (C) 2014 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 159 matching lines @@
     std::generate(testData.begin(), testData.end(), &std::rand);
 
     PurgeableVector purgeableVector(makePurgeableOption());
     purgeableVector.reserveCapacity(kTestSize);
     const char* const data = purgeableVector.data();
 
     purgeableVector.append(testData.data(), testData.size());
     EXPECT_EQ(data, purgeableVector.data());
     EXPECT_EQ(0, memcmp(purgeableVector.data(), testData.data(), testData.size()));
 
-    // Appending one extra byte should cause a reallocation since the first
-    // allocation happened while the purgeable vector was empty. This behavior
-    // helps us guarantee that there is no memory waste on very small vectors
-    // (which SharedBuffer requires).
-    purgeableVector.append(testData.data(), 1);
-    EXPECT_NE(data, purgeableVector.data());
+    // This test is not reliable if the PurgeableVector uses a plain WTF::Vector
+    // for storage, as it does if discardable memory is not supported; the vectors
+    // capacity will always be expanded to fill the PartitionAlloc bucket.
+    if (isDiscardableMemorySupported()) {
+        // Appending one extra byte should cause a reallocation since the first
+        // allocation happened while the purgeable vector was empty. This behavior
+        // helps us guarantee that there is no memory waste on very small vectors
+        // (which SharedBuffer requires).
+        purgeableVector.append(testData.data(), 1);
+        EXPECT_NE(data, purgeableVector.data());
+    }
 }
 
 TEST_P(PurgeableVectorTestWithPlatformSupport, appendReservesCapacityIfNeeded)
 {
     Vector<char> testData(kTestSize);
     std::generate(testData.begin(), testData.end(), &std::rand);
 
     PurgeableVector purgeableVector(makePurgeableOption());
     // No reserveCapacity().
     ASSERT_FALSE(purgeableVector.data());
@@ skipping 127 matching lines @@
         ASSERT_EQ(0, memcmp(purgeableVector.data(), testData.data(), testData.size()));
 }
 
 // Instantiates all the unit tests using the SharedBufferTestWithPlatformSupport fixture both with
 // and without discardable memory support.
 INSTANTIATE_TEST_CASE_P(testsWithPlatformSetUp, PurgeableVectorTestWithPlatformSupport,
     ::testing::Values(DontSupportDiscardableMemory, SupportDiscardableMemory));
 
 } // namespace