Diagnose failing GC transition on forced Oilpan GC.

third_party/WebKit/Source/bindings/core/v8/V8GCController.cpp

Index: third_party/WebKit/Source/bindings/core/v8/V8GCController.cpp
diff --git a/third_party/WebKit/Source/bindings/core/v8/V8GCController.cpp b/third_party/WebKit/Source/bindings/core/v8/V8GCController.cpp
index 801aa58343f679f17581680a5161ca964526af4b..8bd97aaa7fb85a68aeb2d1dc9f7a9e0275a0aba0 100644
--- a/third_party/WebKit/Source/bindings/core/v8/V8GCController.cpp
+++ b/third_party/WebKit/Source/bindings/core/v8/V8GCController.cpp
@@ -382,8 +382,13 @@ void V8GCController::gcEpilogue(v8::Isolate* isolate, v8::GCType type, v8::GCCal
         Heap::collectGarbage(BlinkGC::HeapPointersOnStack, BlinkGC::GCWithSweep, BlinkGC::ForcedGC);
 
         // Forces a precise GC at the end of the current event loop.
-        if (ThreadState::current())
+        if (ThreadState::current()) {
+            // Temporary asserts to diagnose crbug.com/571207's failure to transition
+            // to FullGCScheduled.
+            RELEASE_ASSERT(!ThreadState::current()->isSweepingInProgress());
+            RELEASE_ASSERT(!ThreadState::current()->isInGC());
             ThreadState::current()->setGCState(ThreadState::FullGCScheduled);
+        }
     }
 
     TRACE_EVENT_INSTANT1(TRACE_DISABLED_BY_DEFAULT("devtools.timeline"), "UpdateCounters", TRACE_EVENT_SCOPE_THREAD, "data", InspectorUpdateCountersEvent::data());