[wasm] GrowMemory should update imported memory objects.

test/mjsunit/wasm/import-memory.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: --expose-wasm
 
 load("test/mjsunit/wasm/wasm-constants.js");
 load("test/mjsunit/wasm/wasm-module-builder.js");
 
 (function TestOne() {
@@ skipping 163 matching lines @@
     assertEquals(i * kPageSize, memory.buffer.byteLength);
     for (offset = (i - 1) * kPageSize; offset < i * kPageSize - 3; offset++) {
       store(offset * 2);
     }
   }
   for (offset = 5 * kPageSize; offset < 5 * kPageSize + 4; offset++) {
     assertThrows(load);
   }
   assertThrows(() => memory.grow(16381));
 })();
+
+(function ImportedMemoryBufferLength() {
+  print("ImportedMemoryBufferLength");
+  let memory = new WebAssembly.Memory({initial: 2, maximum: 10});
+  assertEquals(2*kPageSize, memory.buffer.byteLength);
+  let builder = new WasmModuleBuilder();
+  builder.addFunction("grow", kSig_i_i)
+      .addBody([kExprGetLocal, 0, kExprGrowMemory])
+      .exportFunc();
+  builder.addImportedMemory("mine");
+  let instance = builder.instantiate({mine: memory});
+  function grow(pages) { return instance.exports.grow(pages); }
+  assertEquals(2, grow(3));
+  assertEquals(5*kPageSize, memory.buffer.byteLength);
+  assertEquals(5, grow(5));
+  assertEquals(10*kPageSize, memory.buffer.byteLength);
+  assertThrows(() => memory.grow(1));
+})();