Port and integrate the irregexp engine from V8

runtime/vm/flow_graph_optimizer.h

Index: runtime/vm/flow_graph_optimizer.h
diff --git a/runtime/vm/flow_graph_optimizer.h b/runtime/vm/flow_graph_optimizer.h
index 3415b6d45bba6eb4d4727af096b63c1e566b9cff..455f2d0d9dd2276721b2fe6911938ded7423ac38 100644
--- a/runtime/vm/flow_graph_optimizer.h
+++ b/runtime/vm/flow_graph_optimizer.h
@@ -144,6 +144,19 @@ class FlowGraphOptimizer : public FlowGraphVisitor {
                               TargetEntryInstr** entry,
                               Definition** last);
 
+  Definition* PrepareInlineStringIndexOpUnchecked(Instruction* call,
+                                                  intptr_t cid,
+                                                  intptr_t count,
+                                                  Definition* str,
+                                                  Definition* index,
+                                                  Instruction* cursor);
+
+  bool InlineStringCodeUnitsAt(Instruction* call,
+                               intptr_t cid,
+                               intptr_t count,
+                               TargetEntryInstr** entry,
+                               Definition** last);
+
   bool InlineStringBaseCharAt(Instruction* call,
                               intptr_t cid,
                               TargetEntryInstr** entry,