Oilpan: always shrink tail-allocated backing storage (reland.)

third_party/WebKit/Source/platform/heap/HeapAllocator.cpp

Index: third_party/WebKit/Source/platform/heap/HeapAllocator.cpp
diff --git a/third_party/WebKit/Source/platform/heap/HeapAllocator.cpp b/third_party/WebKit/Source/platform/heap/HeapAllocator.cpp
index 8d27428b2d4aa8084f36731368b34a4b7d6827ac..d78e07281424c8f370c82fbab7e680207a49bf0f 100644
--- a/third_party/WebKit/Source/platform/heap/HeapAllocator.cpp
+++ b/third_party/WebKit/Source/platform/heap/HeapAllocator.cpp
@@ -88,14 +88,10 @@ bool HeapAllocator::expandHashTableBacking(void* address, size_t newSize)
 
 bool HeapAllocator::backingShrink(void* address, size_t quantizedCurrentSize, size_t quantizedShrunkSize)
 {
-    // We shrink the object only if the shrinking will make a non-small
-    // prompt-free block.
-    // FIXME: Optimize the threshold size.
-    if (quantizedCurrentSize <= quantizedShrunkSize + sizeof(HeapObjectHeader) + sizeof(void*) * 32)
+    if (!address || quantizedShrunkSize == quantizedCurrentSize)
         return true;
 
-    if (!address)
-        return true;
+    ASSERT(quantizedShrunkSize < quantizedCurrentSize);
 
     ThreadState* state = ThreadState::current();
     if (state->sweepForbidden())
@@ -112,6 +108,12 @@ bool HeapAllocator::backingShrink(void* address, size_t quantizedCurrentSize, si
     HeapObjectHeader* header = HeapObjectHeader::fromPayload(address);
     ASSERT(header->checkHeader());
     NormalPageHeap* heap = static_cast<NormalPage*>(page)->heapForNormalPage();
+    // We shrink the object only if the shrinking will make a non-small
+    // prompt-free block.
+    // FIXME: Optimize the threshold size.
+    if (quantizedCurrentSize <= quantizedShrunkSize + sizeof(HeapObjectHeader) + sizeof(void*) * 32 && !heap->isObjectAllocatedAtAllocationPoint(header))
+        return true;
+
     bool succeededAtAllocationPoint = heap->shrinkObject(header, quantizedShrunkSize);
     if (succeededAtAllocationPoint)
         state->allocationPointAdjusted(heap->heapIndex());