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 4478fbb6b52e085cbaa16a1b2a2ead7318debdd2..0ec8230b157c023ae6da77a249378ce349eb9e29 100644
--- a/Source/platform/heap/ThreadState.cpp
+++ b/Source/platform/heap/ThreadState.cpp
@@ -718,6 +718,10 @@ bool ThreadState::shouldSchedulePreciseGC()
 // These heuristics affect performance significantly.
 bool ThreadState::shouldForceConservativeGC()
 {
+    if (Heap::isGCUrgentlyRequested()) {
+        Heap::clearUrgentGC();

[haraken, 2015/02/10 01:23:17]

We should call Heap::clearUrgentGC() in Heap::collectGarbage(), so that the flag
is cleared when a precise GC runs as well.

+        return true;
+    }
     size_t newSize = Heap::allocatedObjectSize();
     if (newSize >= 300 * 1024 * 1024) {
         // If we consume too much memory, trigger a conservative GC
@@ -743,8 +747,12 @@ void ThreadState::scheduleGCIfNeeded()
     checkThread();
     // Allocation is allowed during sweeping, but those allocations should not
     // trigger nested GCs
-    if (isSweepingInProgress())
-        return;
+    if (isSweepingInProgress()) {
+        if (!Heap::isGCUrgentlyRequested() || !isSweepingScheduled())

[haraken, 2015/02/10 01:23:17]

If an urgent GC is scheduled, I think we can just force completeSweep().

  if (Heap::isGCUrgentlyRequested())
    completeSweep();
  if (isSweepingInProgress())
    return;

[sof, 2015/02/11 15:58:25]

That would happen on entering "StoppingOtherThreads", but sweeping afterwards
makes good sense.

+            return;
+        // Urgent GC requested with only a GC scheduled; fall through
+        // and have it be serviced by a conservative GC.
+    }
     ASSERT(!sweepForbidden());
 
     if (shouldForceConservativeGC())