In background compilation make a copy of Field in order to freeze its state

runtime/vm/assembler_arm.cc

Index: runtime/vm/assembler_arm.cc
diff --git a/runtime/vm/assembler_arm.cc b/runtime/vm/assembler_arm.cc
index 16f266215e24208ccf50bcb69f61f3437608c175..4043fc1ebb84501e089c6ff1e15090ff4ea1731f 100644
--- a/runtime/vm/assembler_arm.cc
+++ b/runtime/vm/assembler_arm.cc
@@ -1565,6 +1565,7 @@ void Assembler::LoadIsolate(Register rd) {
 
 bool Assembler::CanLoadFromObjectPool(const Object& object) const {
   ASSERT(!object.IsICData() || ICData::Cast(object).IsOriginal());
+  ASSERT(!object.IsField() || Field::Cast(object).IsOriginal());
   ASSERT(!Thread::CanLoadFromThread(object));
   if (!constant_pool_allowed()) {
     return false;
@@ -1582,6 +1583,7 @@ void Assembler::LoadObjectHelper(Register rd,
                                  bool is_unique,
                                  Register pp) {
   ASSERT(!object.IsICData() || ICData::Cast(object).IsOriginal());
+  ASSERT(!object.IsField() || Field::Cast(object).IsOriginal());
   // Load common VM constants from the thread. This works also in places where
   // no constant pool is set up (e.g. intrinsic code).
   if (Thread::CanLoadFromThread(object)) {
@@ -1641,6 +1643,7 @@ void Assembler::LoadNativeEntry(Register rd,
 
 void Assembler::PushObject(const Object& object) {
   ASSERT(!object.IsICData() || ICData::Cast(object).IsOriginal());
+  ASSERT(!object.IsField() || Field::Cast(object).IsOriginal());
   LoadObject(IP, object);
   Push(IP);
 }
@@ -1648,6 +1651,7 @@ void Assembler::PushObject(const Object& object) {
 
 void Assembler::CompareObject(Register rn, const Object& object) {
   ASSERT(!object.IsICData() || ICData::Cast(object).IsOriginal());
+  ASSERT(!object.IsField() || Field::Cast(object).IsOriginal());
   ASSERT(rn != IP);
   if (object.IsSmi()) {
     CompareImmediate(rn, reinterpret_cast<int32_t>(object.raw()));
@@ -1907,6 +1911,7 @@ void Assembler::StoreIntoObjectNoBarrier(Register object,
                                          const Object& value,
                                          FieldContent old_content) {
   ASSERT(!value.IsICData() || ICData::Cast(value).IsOriginal());
+  ASSERT(!value.IsField() || Field::Cast(value).IsOriginal());
   ASSERT(value.IsSmi() || value.InVMHeap() ||
          (value.IsOld() && value.IsNotTemporaryScopedHandle()));
   // No store buffer update.
@@ -1920,6 +1925,7 @@ void Assembler::StoreIntoObjectNoBarrierOffset(Register object,
                                                const Object& value,
                                                FieldContent old_content) {
   ASSERT(!value.IsICData() || ICData::Cast(value).IsOriginal());
+  ASSERT(!value.IsField() || Field::Cast(value).IsOriginal());
   int32_t ignored = 0;
   if (Address::CanHoldStoreOffset(kWord, offset - kHeapObjectTag, &ignored)) {
     StoreIntoObjectNoBarrier(object, FieldAddress(object, offset), value,