Link all global contexts into a weak list.

src/objects-visiting.h

Index: src/objects-visiting.h
diff --git a/src/objects-visiting.h b/src/objects-visiting.h
index 90f7ce0b3dfa9e04b2b63bfd9c6b8e06551711d1..ed76cb97ce6a995a062163b00a66ba61001affa5 100644
--- a/src/objects-visiting.h
+++ b/src/objects-visiting.h
@@ -50,6 +50,7 @@ class StaticVisitorBase : public AllStatic {
     kVisitShortcutCandidate,
     kVisitByteArray,
     kVisitFixedArray,
+    kVisitGlobalContext,
 
     // For data objects, JS objects and structs along with generic visitor which
     // can visit object of any size we provide visitors specialized by
@@ -263,6 +264,11 @@ class StaticNewSpaceVisitor : public StaticVisitorBase {
                                          FixedArray::BodyDescriptor,
                                          int>::Visit);
 
+    table_.Register(kVisitGlobalContext,
+                    &FixedBodyVisitor<StaticVisitor,
+                                      Context::ScavengeBodyDescriptor,
+                                      int>::Visit);
+
     table_.Register(kVisitByteArray, &VisitByteArray);
 
     table_.Register(kVisitSharedFunctionInfo,