We mustn't finalize sweeping when V8 started collecting garbage.

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

Index: third_party/WebKit/Source/platform/heap/ThreadState.cpp
diff --git a/third_party/WebKit/Source/platform/heap/ThreadState.cpp b/third_party/WebKit/Source/platform/heap/ThreadState.cpp
index 5dade81422fb90875c853471da1f73fa91d9e779..b1183e984e035d465d211fd7b05364983ba970d5 100644
--- a/third_party/WebKit/Source/platform/heap/ThreadState.cpp
+++ b/third_party/WebKit/Source/platform/heap/ThreadState.cpp
@@ -632,15 +632,6 @@ void ThreadState::scheduleV8FollowupGCIfNeeded(BlinkGC::V8GCType gcType)
 
 void ThreadState::willStartV8GC()
 {
-    // Finish Oilpan's complete sweeping before running a V8 GC.
-    // This will let the GC collect more V8 objects.
-    //
-    // TODO(haraken): It's a bit too late for a major GC to schedule
-    // completeSweep() here, because gcPrologue for a major GC is called
-    // not at the point where the major GC started but at the point where
-    // the major GC requests object grouping.
-    completeSweep();
-
     // The fact that the PageNavigation GC is scheduled means that there is

[sof, 2015/11/20 14:39:37]

This means we cannot do page navigation GCs either.

[jochen (gone - plz use gerrit), 2015/11/20 14:46:18]

hum, right :-/

     // a dead frame. In common cases, a sequence of Oilpan's GC => V8 GC =>
     // Oilpan's GC is needed to collect the dead frame. So we force the