Go generic on polymorphic KeyedLoads with string+other maps

test/mjsunit/regress/regress-crbug-425519.js

Index: test/mjsunit/regress/regress-crbug-425519.js
diff --git a/test/mjsunit/regress/regress-crbug-387636.js b/test/mjsunit/regress/regress-crbug-425519.js
similarity index 63%
copy from test/mjsunit/regress/regress-crbug-387636.js
copy to test/mjsunit/regress/regress-crbug-425519.js
index 1e50ace45a293c8561042f1a09c8fcd505b43dc2..d08e7b91aad89c228321623f27062ab82c29bb3d 100644
--- a/test/mjsunit/regress/regress-crbug-387636.js
+++ b/test/mjsunit/regress/regress-crbug-425519.js
@@ -4,11 +4,12 @@
 
 // Flags: --allow-natives-syntax
 
-function f() {
-  [].indexOf(0x40000000);
+function load(a, i) {
+  return a[i];
 }
 
-f();
-f();
-%OptimizeFunctionOnNextCall(f);
-f();
+load([]);
+load(0);
+load("x", 0);
+%OptimizeFunctionOnNextCall(load);
+load([], 0);