Eliminate special keyed load string stub in favor of uniform handlers.

src/arm64/code-stubs-arm64.cc

Index: src/arm64/code-stubs-arm64.cc
diff --git a/src/arm64/code-stubs-arm64.cc b/src/arm64/code-stubs-arm64.cc
index 35b60f7a6fb41e6dc800a7c4369b2f826d55124e..0788d5f09e1fcd2d2a0b6e809cd9a18f72f66d4e 100644
--- a/src/arm64/code-stubs-arm64.cc
+++ b/src/arm64/code-stubs-arm64.cc
@@ -1422,6 +1422,34 @@ void FunctionPrototypeStub::Generate(MacroAssembler* masm) {
 }
 
 
+void LoadIndexedStringStub::Generate(MacroAssembler* masm) {
+  // Return address is in lr.
+  Label miss;
+
+  Register receiver = LoadDescriptor::ReceiverRegister();
+  Register index = LoadDescriptor::NameRegister();
+  Register result = x0;
+  Register scratch = x3;
+  DCHECK(!scratch.is(receiver) && !scratch.is(index));
+
+  StringCharAtGenerator char_at_generator(receiver, index, scratch, result,
+                                          &miss,  // When not a string.
+                                          &miss,  // When not a number.
+                                          &miss,  // When index out of range.
+                                          STRING_INDEX_IS_ARRAY_INDEX,
+                                          RECEIVER_IS_STRING);
+  char_at_generator.GenerateFast(masm);
+  __ Ret();
+
+  StubRuntimeCallHelper call_helper;
+  char_at_generator.GenerateSlow(masm, call_helper);
+
+  __ Bind(&miss);
+  PropertyAccessCompiler::TailCallBuiltin(
+      masm, PropertyAccessCompiler::MissBuiltin(Code::KEYED_LOAD_IC));
+}
+
+
 void InstanceofStub::Generate(MacroAssembler* masm) {
   // Stack on entry:
   // jssp[0]: function.