Speed-up 'new TypedArray(arrayLike)'.

src/d8.cc

Index: src/d8.cc
diff --git a/src/d8.cc b/src/d8.cc
index 1efe2ae0b407958fc4b2e0632e7597f4ae215fe2..cde8404dcc29b914e5e4114c59f918b55892d914 100644
--- a/src/d8.cc
+++ b/src/d8.cc
@@ -1562,7 +1562,14 @@ static void SetStandaloneFlagsViaCommandLine() {
 
 class ShellArrayBufferAllocator : public v8::ArrayBuffer::Allocator {
  public:
-  virtual void* Allocate(size_t length) { return malloc(length); }
+  virtual void* Allocate(size_t length) {
+    void* result = malloc(length);
+    memset(result, 0, length);
+    return result;
+  }
+  virtual void* AllocateUninitialized(size_t length) {
+    return malloc(length);
+  }
   virtual void Free(void* data) { free(data); }
 };