Allow Oilpan heap objects account for their external allocations.

Source/platform/heap/ThreadState.cpp

Index: Source/platform/heap/ThreadState.cpp
diff --git a/Source/platform/heap/ThreadState.cpp b/Source/platform/heap/ThreadState.cpp
index b2f2f607b8ffa5946229c83e6d037e7788824978..e0f6759ee27b2503ccb34e92f6b90c40bba24e56 100644
--- a/Source/platform/heap/ThreadState.cpp
+++ b/Source/platform/heap/ThreadState.cpp
@@ -671,6 +671,9 @@ bool ThreadState::shouldSchedulePreciseGC()
 // These heuristics affect performance significantly.
 bool ThreadState::shouldForceConservativeGC()
 {
+    if (Heap::isUrgentGCRequested())
+        return true;
+
     size_t newSize = Heap::allocatedObjectSize();
     if (newSize >= 300 * 1024 * 1024) {
         // If we consume too much memory, trigger a conservative GC
@@ -696,13 +699,21 @@ void ThreadState::scheduleGCIfNeeded()
     checkThread();
     // Allocation is allowed during sweeping, but those allocations should not
     // trigger nested GCs
-    if (isSweepingInProgress())
-        return;
+    if (isSweepingInProgress()) {
+        if (!Heap::isUrgentGCRequested() || !isSweepingScheduled())
+            return;
+        // Urgent GC requested with only a GC scheduled; fall through
+        // and have it be serviced by a conservative GC.
+    }
     ASSERT(!sweepForbidden());
 
-    if (shouldForceConservativeGC())
-        Heap::collectGarbage(ThreadState::HeapPointersOnStack, ThreadState::GCWithoutSweep);
-    else if (shouldSchedulePreciseGC())
+    if (shouldForceConservativeGC()) {
+        // If GC is deemed urgent, eagerly sweep and finalize any external allocations right away.
+        GCType gcType = Heap::isUrgentGCRequested() ? GCWithSweep : GCWithoutSweep;
+        Heap::collectGarbage(HeapPointersOnStack, gcType);
+        return;
+    }
+    if (shouldSchedulePreciseGC())
         schedulePreciseGC();
     else if (shouldScheduleIdleGC())
         scheduleIdleGC();