Only reference constant root list entries in the snapshot.

src/mips/macro-assembler-mips.cc

Index: src/mips/macro-assembler-mips.cc
diff --git a/src/mips/macro-assembler-mips.cc b/src/mips/macro-assembler-mips.cc
index ae44b3d4db197cee34996f7e29fba11afb8322e1..1f0c9bf13ad3679843922254e7cc6db40ad1cb58 100644
--- a/src/mips/macro-assembler-mips.cc
+++ b/src/mips/macro-assembler-mips.cc
@@ -86,6 +86,7 @@ void MacroAssembler::LoadRoot(Register destination,
 
 void MacroAssembler::StoreRoot(Register source,
                                Heap::RootListIndex index) {
+  DCHECK(Heap::RootCanBeWrittenAfterInitialization(index));
   sw(source, MemOperand(s6, index << kPointerSizeLog2));
 }
 
@@ -94,6 +95,7 @@ void MacroAssembler::StoreRoot(Register source,
                                Heap::RootListIndex index,
                                Condition cond,
                                Register src1, const Operand& src2) {
+  DCHECK(Heap::RootCanBeWrittenAfterInitialization(index));
   Branch(2, NegateCondition(cond), src1, src2);
   sw(source, MemOperand(s6, index << kPointerSizeLog2));
 }