Oilpan: Allow clearing a vector during pre finalizer to disallocate the backing buffer

third_party/WebKit/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 1499 matching lines @@
     }
     EXPECT_LT(31ul, vector_.Capacity());
 
     for (int i = 0; i < 32; ++i) {
       map_.insert(i + 1, new IntWrapper(i + 1));
     }
     EXPECT_LT(31ul, map_.Capacity());
   }
 
   void Dispose() {
-    // Remove elemets so that vector_ will try to shrink.
-    for (int i = 0; i < 32; ++i) {
+    // Remove all elemets except one so that vector_ will try to shrink.
+    for (int i = 1; i < 32; ++i) {
       vector_.pop_back();
     }
     // Check that vector_ hasn't shrunk.
-    EXPECT_LT(31ul, map_.Capacity());
+    EXPECT_LT(31ul, vector_.Capacity());
+    // Just releasing the backing is allowed.
+    vector_.Clear();
+    EXPECT_EQ(0ul, vector_.Capacity());
 
     // Remove elemets so that map_ will try to shrink.
     for (int i = 0; i < 32; ++i) {
       map_.erase(i + 1);
     }
     // Check that map_ hasn't shrunk.
     EXPECT_LT(31ul, map_.Capacity());
     // Just releasing the backing is allowed.
     map_.Clear();
     EXPECT_EQ(0ul, map_.Capacity());
@@ skipping 5143 matching lines @@
     map.insert(key, IntWrapper::Create(i));
   }
 
   EXPECT_FALSE(string.Impl()->HasOneRef());
   map.Clear();
 
   EXPECT_TRUE(string.Impl()->HasOneRef());
 }
 
 }  // namespace blink