Mojo C++ bindings: some improvements for String16 struct traits.

third_party/WebKit/Source/platform/mojo/CommonCustomTypesStructTraits.cpp

Index: third_party/WebKit/Source/platform/mojo/CommonCustomTypesStructTraits.cpp
diff --git a/third_party/WebKit/Source/platform/mojo/CommonCustomTypesStructTraits.cpp b/third_party/WebKit/Source/platform/mojo/CommonCustomTypesStructTraits.cpp
index a66290f23b8a3af2cf5e8e3bd448a5e6933a75c2..4a7c088d84e648e6e53fcad1a2473c41197abbec 100644
--- a/third_party/WebKit/Source/platform/mojo/CommonCustomTypesStructTraits.cpp
+++ b/third_party/WebKit/Source/platform/mojo/CommonCustomTypesStructTraits.cpp
@@ -4,37 +4,48 @@
 
 #include "platform/mojo/CommonCustomTypesStructTraits.h"
 
-#include "base/strings/latin1_string_conversions.h"
 #include <cstring>
 
 namespace mojo {
 
 // static
-WTF::Vector<uint16_t>
-StructTraits<mojo::common::mojom::String16DataView, ::WTF::String>::data(
-    const ::WTF::String& str) {
-  // TODO(zqzhang): Need to find a way to avoid another memory copy here. A
-  // broader is question is that should sending String16 over mojo be avoided?
-  // See https://crbug.com/653209
-
-  base::string16 str16 = base::Latin1OrUTF16ToUTF16(
-      str.length(), str.is8Bit() ? str.characters8() : nullptr /* latin1 */,
-      str.is8Bit() ? nullptr : str.characters16() /* utf16 */);
-  WTF::Vector<uint16_t> rawData(str16.size());
-  memcpy(rawData.data(), str16.data(), str16.size() * sizeof(uint16_t));
-  return rawData;
+void* StructTraits<common::mojom::String16DataView, WTF::String>::SetUpContext(
+    const WTF::String& input) {
+  // If it is null (i.e., StructTraits<>::IsNull() returns true), this method is
+  // guaranteed not to be called.
+  DCHECK(!input.isNull());
+
+  if (!input.is8Bit())
+    return nullptr;
+
+  return new base::string16(input.characters8(),
+                            input.characters8() + input.length());
+}
+
+// static
+ConstCArray<uint16_t> StructTraits<common::mojom::String16DataView,
+                                   WTF::String>::data(const WTF::String& input,
+                                                      void* context) {
+  auto contextObject = static_cast<base::string16*>(context);
+  DCHECK_EQ(input.is8Bit(), !!contextObject);
+
+  if (contextObject) {
+    return ConstCArray<uint16_t>(
+        contextObject->size(),
+        reinterpret_cast<const uint16_t*>(contextObject->data()));
+  }
+
+  return ConstCArray<uint16_t>(
+      input.length(), reinterpret_cast<const uint16_t*>(input.characters16()));
 }
 
 // static
-bool StructTraits<mojo::common::mojom::String16DataView, ::WTF::String>::Read(
-    mojo::common::mojom::String16DataView data,
-    ::WTF::String* out) {
-  mojo::ArrayDataView<uint16_t> view;
+bool StructTraits<common::mojom::String16DataView, WTF::String>::Read(
+    common::mojom::String16DataView data,
+    WTF::String* out) {
+  ArrayDataView<uint16_t> view;
   data.GetDataDataView(&view);
-  if (view.is_null())
-    return false;
-  *out =
-      ::WTF::String(reinterpret_cast<const UChar*>(view.data()), view.size());
+  *out = WTF::String(reinterpret_cast<const UChar*>(view.data()), view.size());
   return true;
 }