Clobber non-live temporaries on some paths involving a possible slow-path allocation.

runtime/vm/intermediate_language_mips.cc

Index: runtime/vm/intermediate_language_mips.cc
diff --git a/runtime/vm/intermediate_language_mips.cc b/runtime/vm/intermediate_language_mips.cc
index 5ed250cd0742ef767d1f5d9e7711e6f60ae1d474..1a0b7e7ec997fd7f62014d297c0483226deb7c51 100644
--- a/runtime/vm/intermediate_language_mips.cc
+++ b/runtime/vm/intermediate_language_mips.cc
@@ -1994,6 +1994,9 @@ void StoreInstanceFieldInstr::EmitNativeCode(FlowGraphCompiler* compiler) {
       locs()->live_registers()->Add(locs()->in(1));
     }
 
+    // Manually preserve temp which could be clobbered on the slow path.
+    locs()->live_registers()->Add(locs()->temp(0));
+
     {
       __ Bind(&store_double);
       EnsureMutableBox(compiler,