Object.observe: fix observation for optimised in/decrement and compound assignment.

src/hydrogen.cc

Index: src/hydrogen.cc
diff --git a/src/hydrogen.cc b/src/hydrogen.cc
index 7100d3a97ab930e57f7b5d5cd2c186201a31da41..bf508dac28d7aeea2af3cfa3eb5281c7d0f83513 100644
--- a/src/hydrogen.cc
+++ b/src/hydrogen.cc
@@ -5910,7 +5910,7 @@ void HOptimizedGraphBuilder::HandleCompoundAssignment(Assignment* expr) {
       }
 
       HInstruction* store;
-      if (!monomorphic) {
+      if (!monomorphic || map->is_observed()) {
         // If we don't know the monomorphic type, do a generic store.
         CHECK_ALIVE(store = BuildStoreNamedGeneric(object, name, instr));
       } else {
@@ -8265,7 +8265,7 @@ void HOptimizedGraphBuilder::VisitCountOperation(CountOperation* expr) {
       input = Pop();
 
       HInstruction* store;
-      if (!monomorphic) {
+      if (!monomorphic || map->is_observed()) {
         // If we don't know the monomorphic type, do a generic store.
         CHECK_ALIVE(store = BuildStoreNamedGeneric(object, name, after));
       } else {