[turbofan] Bailout if LoadBuffer typing assumption doesn't hold.

test/mjsunit/regress/regress-crbug-589792.js

+// Copyright 2016 the V8 project authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+// Flags: --allow-natives-syntax
+
+var boom = (function(stdlib, foreign, heap) {
+  "use asm";
+  var MEM8 = new stdlib.Uint8Array(heap);
+  var MEM32 = new stdlib.Int32Array(heap);
+  function foo(i, j) {
+    j = MEM8[256];
+    // This following value '10' determines the value of 'rax'
+    MEM32[j >> 10] = 0xabcdefaa;
+    return MEM32[j >> 2] + j
+  }
+  return foo
+})(this, 0, new ArrayBuffer(256));
+%OptimizeFunctionOnNextCall(boom);
+boom(0, 0x1000);