Add unit test for freeing VirtualMemory.

runtime/vm/virtual_memory_test.cc

Index: runtime/vm/virtual_memory_test.cc
===================================================================
--- runtime/vm/virtual_memory_test.cc	(revision 41017)
+++ runtime/vm/virtual_memory_test.cc	(working copy)
@@ -39,4 +39,41 @@
   delete vm;
 }
 
+
+UNIT_TEST_CASE(FreeVirtualMemory) {
+  // Reservations should always be handed back to OS upon destruction.
+  const intptr_t kVirtualMemoryBlockSize = 10 * MB;
+  const intptr_t kIterations = 900;  // Enough to exhaust 32-bit address space.
+  for (intptr_t i = 0; i < kIterations; ++i) {
+    VirtualMemory* vm = VirtualMemory::Reserve(kVirtualMemoryBlockSize);
+    vm->Commit(false);
+    delete vm;
+  }
+  // Check that truncation does not introduce leaks.
+  for (intptr_t i = 0; i < kIterations; ++i) {
+    VirtualMemory* vm = VirtualMemory::Reserve(kVirtualMemoryBlockSize);
+    vm->Commit(false);
+    vm->Truncate(kVirtualMemoryBlockSize / 2, true);
+    delete vm;
+  }
+  for (intptr_t i = 0; i < kIterations; ++i) {
+    VirtualMemory* vm = VirtualMemory::Reserve(kVirtualMemoryBlockSize);
+    vm->Commit(true);
+    vm->Truncate(kVirtualMemoryBlockSize / 2, false);
+    delete vm;
+  }
+  for (intptr_t i = 0; i < kIterations; ++i) {
+    VirtualMemory* vm = VirtualMemory::Reserve(kVirtualMemoryBlockSize);
+    vm->Commit(true);
+    vm->Truncate(0, true);
+    delete vm;
+  }
+  for (intptr_t i = 0; i < kIterations; ++i) {
+    VirtualMemory* vm = VirtualMemory::Reserve(kVirtualMemoryBlockSize);
+    vm->Commit(false);
+    vm->Truncate(0, false);
+    delete vm;
+  }
+}
+
 }  // namespace dart