Oilpan: Implement a GC to take a heap snapshot

Source/platform/heap/HeapTest.cpp

Index: Source/platform/heap/HeapTest.cpp
diff --git a/Source/platform/heap/HeapTest.cpp b/Source/platform/heap/HeapTest.cpp
index 84e87846c2fa4848d103ee37333d8e1a9c7f5aac..f1ae466c8cfde41d0daef4cac9c3ff444fe3a65b 100644
--- a/Source/platform/heap/HeapTest.cpp
+++ b/Source/platform/heap/HeapTest.cpp
@@ -522,6 +522,8 @@ protected:
                     atomicIncrement(&m_gcCount);
                 }
 
+                // Taking snapshot shouldn't have any bad side effect.
+                Heap::collectGarbage(ThreadState::NoHeapPointersOnStack, ThreadState::TakeSnapshot, Heap::ForcedGC);
                 Heap::collectGarbage(ThreadState::NoHeapPointersOnStack, ThreadState::GCWithSweep, Heap::ForcedGC);
                 EXPECT_EQ(wrapper->value(), 0x0bbac0de);
                 EXPECT_EQ((*globalPersistent)->value(), 0x0ed0cabb);
@@ -566,6 +568,8 @@ private:
                     atomicIncrement(&m_gcCount);
                 }
 
+                // Taking snapshot shouldn't have any bad side effect.
+                Heap::collectGarbage(ThreadState::NoHeapPointersOnStack, ThreadState::TakeSnapshot, Heap::ForcedGC);
                 Heap::collectGarbage(ThreadState::NoHeapPointersOnStack, ThreadState::GCWithSweep, Heap::ForcedGC);
                 EXPECT_TRUE(weakMap->isEmpty());
                 EXPECT_TRUE(weakMap2.isEmpty());
@@ -3636,7 +3640,7 @@ TEST(HeapTest, CheckAndMarkPointer)
     // This is a low-level test where we call checkAndMarkPointer. This method
     // causes the object start bitmap to be computed which requires the heap
     // to be in a consistent state (e.g. the free allocation area must be put
-    // into a free list header). However when we call makeConsistentForSweeping it
+    // into a free list header). However when we call makeConsistentForGC it
     // also clears out the freelists so we have to rebuild those before trying
     // to allocate anything again. We do this by forcing a GC after doing the
     // checkAndMarkPointer tests.