WIP: Create a LongStringCollection that transfers long strings with fewer copies.

third_party/WebKit/Source/bindings/core/v8/serialization/LongStringCollection.cpp

Index: third_party/WebKit/Source/bindings/core/v8/serialization/LongStringCollection.cpp
diff --git a/third_party/WebKit/Source/bindings/core/v8/serialization/LongStringCollection.cpp b/third_party/WebKit/Source/bindings/core/v8/serialization/LongStringCollection.cpp
new file mode 100644
index 0000000000000000000000000000000000000000..2d6f189864c8afff41c08f6ab9e76d854196c874
--- /dev/null
+++ b/third_party/WebKit/Source/bindings/core/v8/serialization/LongStringCollection.cpp
@@ -0,0 +1,93 @@
+// Copyright 2017 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "bindings/core/v8/serialization/LongStringCollection.h"
+
+#include "bindings/core/v8/V8Binding.h"
+
+namespace blink {
+
+// Bypass the cache. This StringImpl is definitely not cached.
+static v8::Local<v8::String> makeExternalString(v8::Isolate* isolate,
+                                                const String& string) {
+  if (string.is8Bit()) {
+    WebCoreStringResource8* stringResource = new WebCoreStringResource8(string);
+    v8::Local<v8::String> newString;
+    if (!v8::String::NewExternalOneByte(isolate, stringResource)
+             .ToLocal(&newString)) {
+      delete stringResource;
+      return v8::String::Empty(isolate);
+    }
+    return newString;
+  }
+
+  WebCoreStringResource16* stringResource = new WebCoreStringResource16(string);
+  v8::Local<v8::String> newString;
+  if (!v8::String::NewExternalTwoByte(isolate, stringResource)
+           .ToLocal(&newString)) {
+    delete stringResource;
+    return v8::String::Empty(isolate);
+  }
+  return newString;
+}
+
+LongStringCollection::~LongStringCollection() = default;
+
+Vector<v8::Local<v8::String>> LongStringCollection::getAll(
+    v8::Isolate* isolate) const {
+#if DCHECK_IS_ON()
+  DCHECK(m_v8Strings.isEmpty() || m_isolate == isolate);
+#endif
+
+  Vector<v8::Local<v8::String>> result;
+  switch (m_policy.type()) {
+    case LongStringPolicy::kNone:
+      break;
+
+    case LongStringPolicy::kSameIsolate:
+      result.reserveInitialCapacity(m_v8Strings.size());
+      for (const auto& v8String : m_v8Strings)
+        result.uncheckedAppend(v8String.Get(isolate));
+      break;
+
+    case LongStringPolicy::kSameProcess:
+      result.reserveInitialCapacity(m_wtfStrings.size());
+      for (const auto& wtfString : m_wtfStrings) {
+        result.uncheckedAppend(makeExternalString(isolate, wtfString));
+      }
+      break;
+  }
+  return result;
+}
+
+uint32_t LongStringCollection::put(v8::Isolate* isolate,
+                                   v8::Local<v8::String> string) {
+  DCHECK_GE(string->Length(), m_policy.minimumLength());
+#if DCHECK_IS_ON()
+  DCHECK(!m_isolate || m_isolate == isolate);
+  m_isolate = isolate;
+#endif
+
+  switch (m_policy.type()) {
+    case LongStringPolicy::kNone:
+      NOTREACHED();
+      return 0;
+
+    case LongStringPolicy::kSameIsolate:
+      m_v8Strings.push_back(v8::Global<v8::String>(isolate, string));
+      return m_v8Strings.size() - 1;
+
+    case LongStringPolicy::kSameProcess: {
+      String wtfString =
+          v8StringToWebCoreString<String>(string, DoNotExternalize);
+      if (!wtfString.isSafeToSendToAnotherThread())
+        wtfString = wtfString.isolatedCopy();
+      DCHECK(wtfString.isSafeToSendToAnotherThread());
+      m_wtfStrings.push_back(std::move(wtfString));
+      return m_wtfStrings.size() - 1;
+    }
+  }
+}
+
+}  // namespace blink