IndexedDB: Remove default constructor from IDBValue.

The default constructor is only used in tests, for convenience. It is
not obvious what the semantics should be for such a constructor.

This CL removes the default constructor and introduces a test helper that
creates IDBValue instances.

Bug: 
Change-Id: If8b2cada03afe8cd3ffa58cc6ab711d96b96f013
Reviewed-on: https://chromium-review.googlesource.com/828694
Commit-Queue: Victor Costan <pwnall@chromium.org>
Reviewed-by: Joshua Bell <jsbell@chromium.org>
Cr-Commit-Position: refs/heads/master@{#524501}

third_party/WebKit/Source/modules/indexeddb/IDBRequestTest.cpp

@@ -108,13 +108,14 @@ void EnsureIDBCallbacksDontThrow(IDBRequest* request,
   request->HandleResponse(
       DOMException::Create(kAbortError, "Description goes here."));
   request->HandleResponse(nullptr, IDBKey::CreateInvalid(),
-                          IDBKey::CreateInvalid(), IDBValue::Create());
+                          IDBKey::CreateInvalid(),
+                          CreateNullIDBValueForTesting());
   request->HandleResponse(IDBKey::CreateInvalid());
-  request->HandleResponse(IDBValue::Create());
+  request->HandleResponse(CreateNullIDBValueForTesting());
   request->HandleResponse(static_cast<int64_t>(0));
   request->HandleResponse();
   request->HandleResponse(IDBKey::CreateInvalid(), IDBKey::CreateInvalid(),
-                          IDBValue::Create());
+                          CreateNullIDBValueForTesting());
   request->EnqueueResponse(Vector<String>());
 
   EXPECT_TRUE(!exception_state.HadException());

third_party/WebKit/Source/modules/indexeddb/IDBTestHelper.cpp

@@ -17,6 +17,23 @@
 
 namespace blink {
 
+std::unique_ptr<IDBValue> CreateNullIDBValueForTesting() {
+  scoped_refptr<SerializedScriptValue> null_ssv =
+      SerializedScriptValue::NullValue();
+
+  StringView ssv_wire_bytes = null_ssv->GetWireData();
+  DCHECK(ssv_wire_bytes.Is8Bit());
+
+  scoped_refptr<SharedBuffer> idb_value_buffer = SharedBuffer::Create();
+  idb_value_buffer->Append(
+      reinterpret_cast<const char*>(ssv_wire_bytes.Characters8()),
+      ssv_wire_bytes.length());
+  return IDBValue::Create(std::move(idb_value_buffer),
+                          Vector<scoped_refptr<BlobDataHandle>>(),
+                          Vector<WebBlobInfo>(), IDBKey::CreateNumber(42.0),
+                          IDBKeyPath(String("primaryKey")));
+}
+
 std::unique_ptr<IDBValue> CreateIDBValueForTesting(v8::Isolate* isolate,
                                                    bool create_wrapped_value) {
   size_t element_count = create_wrapped_value ? 16 : 2;

third_party/WebKit/Source/modules/indexeddb/IDBTestHelper.h

@@ -11,6 +11,8 @@
 
 namespace blink {
 
+std::unique_ptr<IDBValue> CreateNullIDBValueForTesting();
+
 // The created value is an array of true. If create_wrapped_value is true, the
 // IDBValue's byte array will be wrapped in a Blob, otherwise it will not be.
 std::unique_ptr<IDBValue> CreateIDBValueForTesting(v8::Isolate*,

third_party/WebKit/Source/modules/indexeddb/IDBValue.cpp

@@ -16,8 +16,6 @@
 
 namespace blink {
 
-IDBValue::IDBValue() = default;
-
 IDBValue::IDBValue(const WebIDBValue& value, v8::Isolate* isolate)
     : IDBValue(value.data,
                value.web_blob_info,
@@ -72,10 +70,6 @@ IDBValue::~IDBValue() {
     isolate_->AdjustAmountOfExternalAllocatedMemory(-external_allocated_size_);
 }
 
-std::unique_ptr<IDBValue> IDBValue::Create() {
-  return WTF::WrapUnique(new IDBValue());
-}
-
 std::unique_ptr<IDBValue> IDBValue::Create(const WebIDBValue& value,
                                            v8::Isolate* isolate) {
   return WTF::WrapUnique(new IDBValue(value, isolate));

third_party/WebKit/Source/modules/indexeddb/IDBValue.h

@@ -24,7 +24,6 @@ struct WebIDBValue;
 
 class MODULES_EXPORT IDBValue final {
  public:
-  static std::unique_ptr<IDBValue> Create();
   static std::unique_ptr<IDBValue> Create(const WebIDBValue&, v8::Isolate*);
 
   // Injects a primary key into a value coming from the backend.
@@ -61,7 +60,6 @@ class MODULES_EXPORT IDBValue final {
 
   friend class IDBValueUnwrapper;
 
-  IDBValue();
   IDBValue(const WebIDBValue&, v8::Isolate*);
   IDBValue(scoped_refptr<SharedBuffer>,
            const WebVector<WebBlobInfo>&,