Ship ES2015 sloppy-mode const semantics

test/mjsunit/regress/regress-1199637.js

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-// Flags: --allow-natives-syntax --es52-globals
+// Flags: --allow-natives-syntax --legacy-const
 
 // Make sure that we can introduce global variables (using
 // both var and const) that shadow even READ_ONLY variables
 // in the prototype chain.
 const NONE = 0;
 const READ_ONLY = 1;
 
 // Use DeclareGlobal...
 %AddNamedProperty(this.__proto__, "a", 1234, NONE);
 assertEquals(1234, a);
@@ skipping 28 matching lines @@
 
 %AddNamedProperty(this.__proto__, "z", 1234, READ_ONLY);
 assertEquals(1234, z);
 eval("with({}) { var z = 5678; }");
 assertEquals(5678, z);
 
 %AddNamedProperty(this.__proto__, "w", 1234, READ_ONLY);
 assertEquals(1234, w);
 eval("with({}) { const w = 5678; }");
 assertEquals(5678, w);