Do not attempt an Oilpan memory pressure GC if nested.

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 9ad69b6a76d7143d461e7cd40a8339f4c8375f84..5dade81422fb90875c853471da1f73fa91d9e779 100644
--- a/third_party/WebKit/Source/platform/heap/ThreadState.cpp
+++ b/third_party/WebKit/Source/platform/heap/ThreadState.cpp
@@ -709,6 +709,10 @@ void ThreadState::scheduleGCIfNeeded()
     if (isGCForbidden())
         return;
 
+    if (isSweepingInProgress())
+        return;
+    ASSERT(!sweepForbidden());
+
     if (shouldForceMemoryPressureGC()) {
         completeSweep();
         if (shouldForceMemoryPressureGC()) {
@@ -720,10 +724,6 @@ void ThreadState::scheduleGCIfNeeded()
         }
     }
 
-    if (isSweepingInProgress())
-        return;
-    ASSERT(!sweepForbidden());
-
     if (shouldForceConservativeGC()) {
         completeSweep();
         if (shouldForceConservativeGC()) {