Intrinsify ExternalUint8Array.[].

runtime/vm/intrinsifier_x64.cc

Index: runtime/vm/intrinsifier_x64.cc
diff --git a/runtime/vm/intrinsifier_x64.cc b/runtime/vm/intrinsifier_x64.cc
index 5f3f96d8e5b114a0b0cf5ff58e4b5a6e36ffdc75..e5dd2b404a8b3a05d09cea8633227cf100ecabae 100644
--- a/runtime/vm/intrinsifier_x64.cc
+++ b/runtime/vm/intrinsifier_x64.cc
@@ -700,6 +700,20 @@ bool Intrinsifier::Float64Array_setIndexed(Assembler* assembler) {
 }
 
 
+bool Intrinsifier::ExternalUint8Array_getIndexed(Assembler* assembler) {
+  Label fall_through;
+  TestByteArrayIndex(assembler, &fall_through);
+  __ SmiUntag(R12);
+  __ movq(RAX, FieldAddress(RAX, ExternalUint8Array::external_data_offset()));
+  __ movq(RAX, Address(RAX, ExternalByteArrayData<uint8_t>::data_offset()));
+  __ movzxb(RAX, Address(RAX, R12, TIMES_1, 0));
+  __ SmiTag(RAX);
+  __ ret();
+  __ Bind(&fall_through);
+  return false;
+}
+
+
 // Tests if two top most arguments are smis, jumps to label not_smi if not.
 // Topmost argument is in RAX.
 static void TestBothArgumentsSmis(Assembler* assembler, Label* not_smi) {