Fix bug with optimized try-catch on ARM/MIPS.

runtime/vm/flow_graph_compiler_arm.cc

Index: runtime/vm/flow_graph_compiler_arm.cc
===================================================================
--- runtime/vm/flow_graph_compiler_arm.cc	(revision 25871)
+++ runtime/vm/flow_graph_compiler_arm.cc	(working copy)
@@ -790,10 +790,9 @@
   }
 
   // Process locals. Skip exception_var and stacktrace_var.
-  CatchEntryInstr* catch_entry = catch_block->next()->AsCatchEntry();
   intptr_t local_base = kFirstLocalSlotFromFp + num_non_copied_params;
-  intptr_t ex_idx = local_base - catch_entry->exception_var().index();
-  intptr_t st_idx = local_base - catch_entry->stacktrace_var().index();
+  intptr_t ex_idx = local_base - catch_block->exception_var().index();
+  intptr_t st_idx = local_base - catch_block->stacktrace_var().index();
   for (; i < flow_graph().variable_count(); ++i) {
     if (i == ex_idx || i == st_idx) continue;
     if ((*idefs)[i]->IsConstant()) continue;