[wasm] Implement importing of WebAssembly.Memory.

test/mjsunit/wasm/wasm-module-builder.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.
 
 // Used for encoding f32 and double constants to bits.
 let __buffer = new ArrayBuffer(8);
 let byte_view = new Int8Array(__buffer);
 let f32_view = new Float32Array(__buffer);
 let f64_view = new Float64Array(__buffer);
 
@@ skipping 176 matching lines @@
     return this.addImportWithModule(name, undefined, type);
   }
 
   addImportedGlobal(module, name, type) {
     let o = {module: module, name: name, kind: kExternalGlobal, type: type,
              mutable: false}
     this.imports.push(o);
     return this.num_imported_globals++;
   }
 
+  addImportedMemory(module, name, initial = 0, maximum) {
+    let o = {module: module, name: name, kind: kExternalMemory, initial: initial, maximum: maximum};
+    this.imports.push(o);
+  }
+
   addDataSegment(addr, data, init) {
     this.segments.push({addr: addr, data: data, init: init});
     return this.segments.length - 1;
   }
 
+  exportMemoryAs(name) {
+    this.exports.push({name: name, kind: kExternalMemory, index: 0});
+  }
+
   appendToTable(array) {
     this.table.push(...array);
     return this;
   }
 
   toArray(debug) {
     let binary = new Binary;
     let wasm = this;
 
     // Add header
@@ skipping 25 matching lines @@
         section.emit_u32v(wasm.imports.length);
         for (let imp of wasm.imports) {
           section.emit_string(imp.module);
           section.emit_string(imp.name || '');
           section.emit_u8(imp.kind);
           if (imp.kind == kExternalFunction) {
             section.emit_u32v(imp.type);
           } else if (imp.kind == kExternalGlobal) {
             section.emit_u32v(imp.type);
             section.emit_u8(imp.mutable);
+          } else if (imp.kind == kExternalMemory) {
+            var has_max = (typeof imp.maximum) != "undefined";
+            section.emit_u8(has_max ? 1 : 0); // flags
+            section.emit_u32v(imp.initial); // initial
+            if (has_max) section.emit_u32v(imp.maximum); // maximum
           } else {
             throw new Error("unknown/unsupported import kind " + imp.kind);
           }
         }
       });
     }
 
     // Add functions declarations
     let has_names = false;
     let names = false;
@@ skipping 216 matching lines @@
     }
     return buffer;
   }
 
   instantiate(...args) {
     let module = new WebAssembly.Module(this.toBuffer());
     let instance = new WebAssembly.Instance(module, ...args);
     return instance;
   }
 }