Partially revert r26703 and omit regular code generation for implicit accessors.

runtime/vm/flow_graph_compiler_arm64.cc

Index: runtime/vm/flow_graph_compiler_arm64.cc
diff --git a/runtime/vm/flow_graph_compiler_arm64.cc b/runtime/vm/flow_graph_compiler_arm64.cc
index 76da1808b299bcec12649b6f4babd157e4ffaf1c..3cb52a1a67e0fd8ddd93482dcde736007b3d7053 100644
--- a/runtime/vm/flow_graph_compiler_arm64.cc
+++ b/runtime/vm/flow_graph_compiler_arm64.cc
@@ -1022,7 +1022,10 @@ void FlowGraphCompiler::EmitFrameEntry() {
 void FlowGraphCompiler::CompileGraph() {
   InitCompiler();
 
-  TryIntrinsify();
+  if (TryIntrinsify()) {
+    // Intrinsic has no fall through.
+    return;
+  }
 
   EmitFrameEntry();
   ASSERT(assembler()->constant_pool_allowed());