Mojo C++ bindings: support mapping mojo string to WTF::String.

The generator now supports a "--for_blink" flag. When it is specified, the generator will map mojo string to WTF::String.

BUG=583738

Review URL: https://codereview.chromium.org/1751563002

Cr-Commit-Position: refs/heads/master@{#381091}

31 files changed, 574 insertions, 44 deletions

diff --git a/mojo/mojo_edk_tests.gyp b/mojo/mojo_edk_tests.gyp
index b8ff828..e1a51de 100644
--- a/mojo/mojo_edk_tests.gyp
+++ b/mojo/mojo_edk_tests.gyp
@@ -101,6 +101,21 @@
       ],
     },
     {
+      # GN version: //mojo/public/cpp/bindings/tests:for_blink_tests
+      'target_name': 'mojo_public_bindings_for_blink_tests',
+      'type': 'static_library',
+      'dependencies': [
+        '../testing/gtest.gyp:gtest',
+        'mojo_public.gyp:mojo_cpp_bindings',
+        'mojo_public.gyp:mojo_public_test_utils',
+        'mojo_public.gyp:mojo_public_test_wtf_types',
+        'mojo_public.gyp:mojo_public_test_wtf_types_blink',
+      ],
+      'sources': [
+        'public/cpp/bindings/tests/wtf_types_unittest.cc',
+      ],
+    },
+    {
       # GN version: //mojo/edk/test:mojo_public_bindings_perftests
       'target_name': 'mojo_public_bindings_perftests',
       'type': 'executable',
diff --git a/mojo/mojo_public.gyp b/mojo/mojo_public.gyp
index 2844195..da318ae 100644
--- a/mojo/mojo_public.gyp
+++ b/mojo/mojo_public.gyp
@@ -177,6 +177,9 @@
         'public/cpp/bindings/lib/validation_util.cc',
         'public/cpp/bindings/lib/validation_util.h',
         'public/cpp/bindings/lib/value_traits.h',
+        # Include the .h but not the .cc file. The .h file is used by
+        # serialization_forward.h.
+        'public/cpp/bindings/lib/wtf_string_serialization.h',
         'public/cpp/bindings/message.h',
         'public/cpp/bindings/message_filter.h',
         'public/cpp/bindings/no_interface.h',
@@ -194,6 +197,33 @@
       ],
     },
     {
+      # GN version: //mojo/public/cpp/bindings:wtf_support
+      'target_name': 'mojo_cpp_bindings_wtf_support',
+      'type': 'static_library',
+      'include_dirs': [
+        '..'
+      ],
+      'sources': [
+        'public/cpp/bindings/lib/wtf_serialization.h',
+        'public/cpp/bindings/lib/wtf_string_serialization.cc',
+        'public/cpp/bindings/lib/wtf_string_serialization.h',
+      ],
+      'dependencies': [
+        'mojo_cpp_bindings',
+        '../third_party/WebKit/Source/config.gyp:config',
+        '../third_party/WebKit/Source/wtf/wtf.gyp:wtf',
+      ],
+      'export_dependent_settings': [
+        'mojo_cpp_bindings',
+        '../third_party/WebKit/Source/config.gyp:config',
+      ],
+      'direct_dependent_settings': {
+        'variables': {
+          'clang_warning_flags_unset': [ '-Wglobal-constructors' ],
+        },
+      },
+    },
+    {
       # GN version: //mojo/message_pump
       'target_name': 'mojo_message_pump_lib',
       'type': '<(component)',
@@ -456,6 +486,26 @@
         'mojo_cpp_bindings',
       ],
     },
+    {
+      'target_name': 'mojo_public_test_wtf_types',
+      'type': 'static_library',
+      'sources': [
+        'public/interfaces/bindings/tests/test_wtf_types.mojom',
+      ],
+      'includes': [ 'mojom_bindings_generator.gypi' ],
+    },
+    {
+      'target_name': 'mojo_public_test_wtf_types_blink',
+      'type': 'static_library',
+      'variables': {
+        'mojom_variant': 'blink',
+        'for_blink': 'true',
+      },
+      'sources': [
+        'public/interfaces/bindings/tests/test_wtf_types.mojom',
+      ],
+      'includes': [ 'mojom_bindings_generator.gypi' ],
+    },
   ],
   'conditions': [
     ['OS == "android"', {
diff --git a/mojo/mojom_bindings_generator.gypi b/mojo/mojom_bindings_generator.gypi
index 3b2e1bb..6518ee4 100644
--- a/mojo/mojom_bindings_generator.gypi
+++ b/mojo/mojom_bindings_generator.gypi
@@ -11,10 +11,12 @@
       'mojom_typemap_dependencies%': [],
       'mojom_typemaps%': [],
       'mojom_variant%': 'none',
+      'for_blink%': 'false',
     },
     'mojom_typemap_dependencies%': ['<@(mojom_typemap_dependencies)'],
     'mojom_typemaps%': ['<@(mojom_typemaps)'],
     'mojom_variant%': '<(mojom_variant)',
+    'for_blink%': '<(for_blink)',
     'mojom_base_output_dir':
         '<!(python <(DEPTH)/build/inverse_depth.py <(DEPTH))',
     'mojom_generated_outputs': [
@@ -30,6 +32,18 @@
       }, {
         'mojom_output_languages%': 'c++',
       }],
+      ['for_blink=="true"', {
+        'mojom_generator_wtf_arg%': [
+          '--for_blink',
+        ],
+        'wtf_dependencies%': [
+          'mojo_public.gyp:mojo_cpp_bindings_wtf_support',
+          '../third_party/WebKit/Source/wtf/wtf.gyp:wtf',
+        ],
+      }, {
+        'mojom_generator_wtf_arg%': [],
+        'wtf_dependencies%': [],
+      }],
     ],
   },
   'actions': [
@@ -98,6 +112,7 @@
         '-g', '<(mojom_output_languages)',
         '<@(mojom_generator_typemap_args)',
         '<@(mojom_extra_generator_args)',
+        '<@(mojom_generator_wtf_arg)',
         '--bytecode_path',
         '<(SHARED_INTERMEDIATE_DIR)/mojo/public/tools/bindings',
       ],
@@ -110,9 +125,11 @@
     '<(DEPTH)/mojo/mojo_public.gyp:mojo_interface_bindings_generation',
     '<(DEPTH)/mojo/public/tools/bindings/bindings.gyp:precompile_mojom_bindings_generator_templates',
     '<@(mojom_typemap_dependencies)',
+    '<@(wtf_dependencies)',
   ],
   'export_dependent_settings': [
     '<@(mojom_typemap_dependencies)',
+    '<@(wtf_dependencies)',
   ],
   'include_dirs': [
     '<(DEPTH)',
diff --git a/mojo/mojom_bindings_generator_explicit.gypi b/mojo/mojom_bindings_generator_explicit.gypi
index 319c4ff..0ca10c6 100644
--- a/mojo/mojom_bindings_generator_explicit.gypi
+++ b/mojo/mojom_bindings_generator_explicit.gypi
@@ -9,8 +9,10 @@
   'variables': {
     'variables': {
       'mojom_variant%': 'none',
+      'for_blink%': 'false',
     },
     'mojom_variant%': '<(mojom_variant)',
+    'for_blink%': '<(for_blink)',
     'mojom_base_output_dir':
         '<!(python <(DEPTH)/build/inverse_depth.py <(DEPTH))',
     'mojom_generated_outputs': [
@@ -25,6 +27,18 @@
       }, {
         'mojom_output_languages%': 'c++',
       }],
+      ['for_blink=="true"', {
+        'mojom_generator_wtf_arg%': [
+          '--for_blink',
+        ],
+        'wtf_dependencies%': [
+          'mojo_public.gyp:mojo_cpp_bindings_wtf_support',
+          '../third_party/WebKit/Source/wtf/wtf.gyp:wtf',
+        ],
+      }, {
+        'mojom_generator_wtf_arg%': [],
+        'wtf_dependencies%': [],
+      }],
     ],
   },
   # Given mojom files as inputs, generate sources.  These sources will be
@@ -83,6 +97,7 @@
         '--variant', '<(mojom_variant)',
         '-g', '<(mojom_output_languages)',
         '<@(mojom_extra_generator_args)',
+        '<@(mojom_generator_wtf_arg)',
         '--bytecode_path',
         '<(SHARED_INTERMEDIATE_DIR)/mojo/public/tools/bindings',
       ],
@@ -99,6 +114,10 @@
   ],
   'dependencies': [
     '<(DEPTH)/mojo/public/tools/bindings/bindings.gyp:precompile_mojom_bindings_generator_templates',
+    '<@(wtf_dependencies)',
+  ],
+  'export_dependent_settings': [
+    '<@(wtf_dependencies)',
   ],
   # Prevent the generated sources from being injected into the "all" target by
   # preventing the code generator from being directly depended on by the "all"
diff --git a/mojo/public/cpp/bindings/BUILD.gn b/mojo/public/cpp/bindings/BUILD.gn
index 0486a52..1939ff6 100644
--- a/mojo/public/cpp/bindings/BUILD.gn
+++ b/mojo/public/cpp/bindings/BUILD.gn
@@ -81,6 +81,10 @@ source_set("bindings") {
     "lib/validation_util.cc",
     "lib/validation_util.h",
     "lib/value_traits.h",
+
+    # Include the .h but not the .cc file. The .h file is used by
+    # serialization_forward.h.
+    "lib/wtf_string_serialization.h",
     "map.h",
     "message.h",
     "message_filter.h",
@@ -120,3 +124,18 @@ source_set("callback") {
     "//mojo/public/cpp/system",
   ]
 }
+
+source_set("wtf_support") {
+  sources = [
+    "lib/wtf_serialization.h",
+    "lib/wtf_string_serialization.cc",
+    "lib/wtf_string_serialization.h",
+  ]
+
+  public_deps = [
+    ":bindings",
+    "//third_party/WebKit/Source/wtf",
+  ]
+
+  public_configs = [ "//third_party/WebKit/Source:config" ]
+}
diff --git a/mojo/public/cpp/bindings/DEPS b/mojo/public/cpp/bindings/DEPS
new file mode 100644
index 0000000..36eba44
--- /dev/null
+++ b/mojo/public/cpp/bindings/DEPS
@@ -0,0 +1,3 @@
+include_rules = [
+  "+third_party/WebKit/Source/wtf",
+]
diff --git a/mojo/public/cpp/bindings/lib/array_serialization_traits.h b/mojo/public/cpp/bindings/lib/array_serialization_traits.h
index e73d352..35b12f1 100644
--- a/mojo/public/cpp/bindings/lib/array_serialization_traits.h
+++ b/mojo/public/cpp/bindings/lib/array_serialization_traits.h
@@ -19,6 +19,10 @@
 #include "mojo/public/cpp/bindings/lib/template_util.h"
 #include "mojo/public/cpp/bindings/lib/validation_errors.h"
 
+namespace WTF {
+class String;
+}
+
 namespace mojo {
 namespace internal {
 
@@ -191,7 +195,8 @@ struct ArraySerializer<
  private:
   template <typename T,
             bool is_array = IsSpecializationOf<Array, T>::value,
-            bool is_string = std::is_same<T, String>::value>
+            bool is_string = std::is_same<T, String>::value ||
+                             std::is_same<T, WTF::String>::value>
   struct SerializeCaller {
     static void Run(T input,
                     Buffer* buf,
diff --git a/mojo/public/cpp/bindings/lib/bindings_internal.h b/mojo/public/cpp/bindings/lib/bindings_internal.h
index a467acd..8d32082 100644
--- a/mojo/public/cpp/bindings/lib/bindings_internal.h
+++ b/mojo/public/cpp/bindings/lib/bindings_internal.h
@@ -11,6 +11,9 @@
 #include "mojo/public/cpp/bindings/lib/template_util.h"
 #include "mojo/public/cpp/system/core.h"
 
+namespace WTF {
+class String;
+}
 namespace mojo {
 class String;
 
@@ -162,6 +165,11 @@ struct WrapperTraits<String, false> {
   typedef String_Data* DataType;
 };
 
+template <>
+struct WrapperTraits<WTF::String, false> {
+  typedef String_Data* DataType;
+};
+
 }  // namespace internal
 }  // namespace mojo
 
diff --git a/mojo/public/cpp/bindings/lib/bindings_serialization.h b/mojo/public/cpp/bindings/lib/bindings_serialization.h
index 017448b..7a10b1c 100644
--- a/mojo/public/cpp/bindings/lib/bindings_serialization.h
+++ b/mojo/public/cpp/bindings/lib/bindings_serialization.h
@@ -112,6 +112,11 @@ inline void AssociatedInterfaceDataToPtrInfo(
   output->set_version(input->version);
 }
 
+class WTFStringContext {
+ public:
+  virtual ~WTFStringContext() {}
+};
+
 // Context information for serialization/deserialization routines.
 struct SerializationContext {
   SerializationContext();
@@ -121,6 +126,8 @@ struct SerializationContext {
 
   // Used to serialize/deserialize associated interface pointers and requests.
   scoped_refptr<MultiplexRouter> router;
+
+  scoped_ptr<WTFStringContext> wtf_string_context;
 };
 
 }  // namespace internal
diff --git a/mojo/public/cpp/bindings/lib/serialization_forward.h b/mojo/public/cpp/bindings/lib/serialization_forward.h
index 1f809b0..39d046c 100644
--- a/mojo/public/cpp/bindings/lib/serialization_forward.h
+++ b/mojo/public/cpp/bindings/lib/serialization_forward.h
@@ -8,10 +8,12 @@
 #include <stddef.h>
 
 #include "mojo/public/cpp/bindings/lib/string_serialization.h"
+#include "mojo/public/cpp/bindings/lib/wtf_string_serialization.h"
 
 // This file is included by serialization implementation files to avoid circular
 // includes.
-// Users of the serialization funtions should include serialization.h.
+// Users of the serialization funtions should include serialization.h (and also
+// wtf_serialization.h if necessary).
 
 namespace mojo {
 
diff --git a/mojo/public/cpp/bindings/lib/wtf_serialization.h b/mojo/public/cpp/bindings/lib/wtf_serialization.h
new file mode 100644
index 0000000..11733ec
--- /dev/null
+++ b/mojo/public/cpp/bindings/lib/wtf_serialization.h
@@ -0,0 +1,10 @@
+// Copyright 2016 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.
+
+#ifndef MOJO_PUBLIC_CPP_BINDINGS_LIB_WTF_SERIALIZATION_H_
+#define MOJO_PUBLIC_CPP_BINDINGS_LIB_WTF_SERIALIZATION_H_
+
+#include "mojo/public/cpp/bindings/lib/wtf_string_serialization.h"
+
+#endif  // MOJO_PUBLIC_CPP_BINDINGS_LIB_WTF_SERIALIZATION_H_
diff --git a/mojo/public/cpp/bindings/lib/wtf_string_serialization.cc b/mojo/public/cpp/bindings/lib/wtf_string_serialization.cc
new file mode 100644
index 0000000..d1b749d
--- /dev/null
+++ b/mojo/public/cpp/bindings/lib/wtf_string_serialization.cc
@@ -0,0 +1,119 @@
+// Copyright 2016 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 "mojo/public/cpp/bindings/lib/wtf_string_serialization.h"
+
+#include <string.h>
+
+#include <queue>
+
+#include "base/logging.h"
+#include "third_party/WebKit/Source/wtf/text/StringUTF8Adaptor.h"
+#include "third_party/WebKit/Source/wtf/text/WTFString.h"
+
+namespace WTF {
+namespace {
+
+struct UTF8AdaptorWithPointer {
+  explicit UTF8AdaptorWithPointer(const WTF::String& input)
+      : utf8_adaptor(input) {
+#if DCHECK_IS_ON()
+    original_input = reinterpret_cast<uintptr_t>(&input);
+#endif
+  }
+
+  ~UTF8AdaptorWithPointer() {}
+
+  WTF::StringUTF8Adaptor utf8_adaptor;
+
+#if DCHECK_IS_ON()
+  // For sanity check only. Never dereferenced.
+  uintptr_t original_input;
+#endif
+};
+
+class WTFStringContextImpl : public mojo::internal::WTFStringContext {
+ public:
+  WTFStringContextImpl() {}
+  ~WTFStringContextImpl() override {}
+
+  std::queue<UTF8AdaptorWithPointer>& utf8_adaptors() { return utf8_adaptors_; }
+
+ private:
+  // When serializing an object, we call GetSerializedSize_() recursively on
+  // all its elements/members to compute the total size, and then call
+  // Serialize*_() recursively in the same order to do the actual
+  // serialization. If some WTF::Strings need to be converted to UTF8, we don't
+  // want to do that twice. Therefore, we store a WTF::StringUTF8Adaptor for
+  // each in the first pass, and reuse it in the second pass.
+  std::queue<UTF8AdaptorWithPointer> utf8_adaptors_;
+
+  DISALLOW_COPY_AND_ASSIGN(WTFStringContextImpl);
+};
+
+}  // namespace
+
+size_t GetSerializedSize_(const WTF::String& input,
+                          mojo::internal::SerializationContext* context) {
+  if (input.isNull())
+    return 0;
+
+  if (!context->wtf_string_context)
+    context->wtf_string_context.reset(new WTFStringContextImpl);
+
+  auto& utf8_adaptors =
+      static_cast<WTFStringContextImpl*>(context->wtf_string_context.get())
+          ->utf8_adaptors();
+
+  utf8_adaptors.emplace(input);
+
+  return mojo::internal::Align(sizeof(mojo::internal::String_Data) +
+                               utf8_adaptors.back().utf8_adaptor.length());
+}
+
+void Serialize_(const WTF::String& input,
+                mojo::internal::Buffer* buf,
+                mojo::internal::String_Data** output,
+                mojo::internal::SerializationContext* context) {
+  if (input.isNull()) {
+    *output = nullptr;
+    return;
+  }
+
+  auto& utf8_adaptors =
+      static_cast<WTFStringContextImpl*>(context->wtf_string_context.get())
+          ->utf8_adaptors();
+
+  DCHECK(!utf8_adaptors.empty());
+#if DCHECK_IS_ON()
+  DCHECK_EQ(utf8_adaptors.front().original_input,
+            reinterpret_cast<uintptr_t>(&input));
+#endif
+
+  const WTF::StringUTF8Adaptor& adaptor = utf8_adaptors.front().utf8_adaptor;
+
+  mojo::internal::String_Data* result =
+      mojo::internal::String_Data::New(adaptor.length(), buf);
+  if (result)
+    memcpy(result->storage(), adaptor.data(), adaptor.length());
+
+  utf8_adaptors.pop();
+
+  *output = result;
+}
+
+bool Deserialize_(mojo::internal::String_Data* input,
+                  WTF::String* output,
+                  mojo::internal::SerializationContext* context) {
+  if (input) {
+    WTF::String result = WTF::String::fromUTF8(input->storage(), input->size());
+    output->swap(result);
+  } else if (!output->isNull()) {
+    WTF::String result;
+    output->swap(result);
+  }
+  return true;
+}
+
+}  // namespace WTF
diff --git a/mojo/public/cpp/bindings/lib/wtf_string_serialization.h b/mojo/public/cpp/bindings/lib/wtf_string_serialization.h
new file mode 100644
index 0000000..a110265
--- /dev/null
+++ b/mojo/public/cpp/bindings/lib/wtf_string_serialization.h
@@ -0,0 +1,28 @@
+// Copyright 2016 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.
+
+#ifndef MOJO_PUBLIC_CPP_BINDINGS_LIB_WTF_STRING_SERIALIZATION_H_
+#define MOJO_PUBLIC_CPP_BINDINGS_LIB_WTF_STRING_SERIALIZATION_H_
+
+#include <stddef.h>
+
+#include "mojo/public/cpp/bindings/lib/array_internal.h"
+#include "mojo/public/cpp/bindings/lib/bindings_serialization.h"
+
+namespace WTF {
+class String;
+
+size_t GetSerializedSize_(const WTF::String& input,
+                          mojo::internal::SerializationContext* context);
+void Serialize_(const WTF::String& input,
+                mojo::internal::Buffer* buffer,
+                mojo::internal::String_Data** output,
+                mojo::internal::SerializationContext* context);
+bool Deserialize_(mojo::internal::String_Data* input,
+                  WTF::String* output,
+                  mojo::internal::SerializationContext* context);
+
+}  // namespace WTF
+
+#endif  // MOJO_PUBLIC_CPP_BINDINGS_LIB_WTF_STRING_SERIALIZATION_H_
diff --git a/mojo/public/cpp/bindings/tests/BUILD.gn b/mojo/public/cpp/bindings/tests/BUILD.gn
index c689fe31..6a516bb 100644
--- a/mojo/public/cpp/bindings/tests/BUILD.gn
+++ b/mojo/public/cpp/bindings/tests/BUILD.gn
@@ -68,6 +68,24 @@ source_set("tests") {
   ]
 }
 
+source_set("for_blink_tests") {
+  testonly = true
+
+  sources = [
+    "wtf_types_unittest.cc",
+  ]
+
+  deps = [
+    "//mojo/public/cpp/bindings",
+    "//mojo/public/cpp/bindings:callback",
+    "//mojo/public/cpp/system",
+    "//mojo/public/cpp/test_support:test_utils",
+    "//mojo/public/interfaces/bindings/tests:test_wtf_types",
+    "//mojo/public/interfaces/bindings/tests:test_wtf_types_blink",
+    "//testing/gtest",
+  ]
+}
+
 source_set("perftests") {
   testonly = true
 
diff --git a/mojo/public/cpp/bindings/tests/pickle_unittest.cc b/mojo/public/cpp/bindings/tests/pickle_unittest.cc
index bc77298..17b1724 100644
--- a/mojo/public/cpp/bindings/tests/pickle_unittest.cc
+++ b/mojo/public/cpp/bindings/tests/pickle_unittest.cc
@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-#include <string.h>
-
 #include <string>
 
 #include "base/bind.h"
@@ -15,6 +13,7 @@
 #include "mojo/public/cpp/bindings/interface_request.h"
 #include "mojo/public/cpp/bindings/tests/pickled_struct_blink.h"
 #include "mojo/public/cpp/bindings/tests/pickled_struct_chromium.h"
+#include "mojo/public/cpp/bindings/tests/variant_test_util.h"
 #include "mojo/public/interfaces/bindings/tests/test_native_types.mojom-blink.h"
 #include "mojo/public/interfaces/bindings/tests/test_native_types.mojom-chromium.h"
 #include "testing/gtest/include/gtest/gtest.h"
@@ -23,19 +22,6 @@ namespace mojo {
 namespace test {
 namespace {
 
-// Converts a request of Interface1 to a request of Interface0. Interface0 and
-// Interface1 are expected to be two variants of the same mojom interface.
-// In real-world use cases, users shouldn't need to worry about this. Because it
-// is rare to deal with two variants of the same interface in the same app.
-template <typename Interface0, typename Interface1>
-InterfaceRequest<Interface0> ConvertInterfaceRequest(
-    InterfaceRequest<Interface1> request) {
-  DCHECK_EQ(0, strcmp(Interface0::Name_, Interface1::Name_));
-  InterfaceRequest<Interface0> result;
-  result.Bind(request.PassMessagePipe());
-  return result;
-}
-
 template <typename T>
 void DoExpectResult(int foo,
                     int bar,
diff --git a/mojo/public/cpp/bindings/tests/struct_traits_unittest.cc b/mojo/public/cpp/bindings/tests/struct_traits_unittest.cc
index e1ffacb..cd99785 100644
--- a/mojo/public/cpp/bindings/tests/struct_traits_unittest.cc
+++ b/mojo/public/cpp/bindings/tests/struct_traits_unittest.cc
@@ -12,6 +12,7 @@
 #include "mojo/public/cpp/bindings/tests/rect_blink.h"
 #include "mojo/public/cpp/bindings/tests/rect_chromium.h"
 #include "mojo/public/cpp/bindings/tests/struct_with_traits_impl.h"
+#include "mojo/public/cpp/bindings/tests/variant_test_util.h"
 #include "mojo/public/interfaces/bindings/tests/struct_with_traits.mojom.h"
 #include "mojo/public/interfaces/bindings/tests/test_native_types.mojom-blink.h"
 #include "mojo/public/interfaces/bindings/tests/test_native_types.mojom-chromium.h"
@@ -21,19 +22,6 @@ namespace mojo {
 namespace test {
 namespace {
 
-// Converts a request of Interface1 to a request of Interface0. Interface0 and
-// Interface1 are expected to be two variants of the same mojom interface.
-// In real-world use cases, users shouldn't need to worry about this. Because it
-// is rare to deal with two variants of the same interface in the same app.
-template <typename Interface0, typename Interface1>
-InterfaceRequest<Interface0> ConvertInterfaceRequest(
-    InterfaceRequest<Interface1> request) {
-  DCHECK_EQ(0, strcmp(Interface0::Name_, Interface1::Name_));
-  InterfaceRequest<Interface0> result;
-  result.Bind(request.PassMessagePipe());
-  return result;
-}
-
 template <typename T>
 void DoExpectResult(const T& expected,
                     const base::Closure& callback,
diff --git a/mojo/public/cpp/bindings/tests/variant_test_util.h b/mojo/public/cpp/bindings/tests/variant_test_util.h
new file mode 100644
index 0000000..3f6b1f1
--- /dev/null
+++ b/mojo/public/cpp/bindings/tests/variant_test_util.h
@@ -0,0 +1,32 @@
+// Copyright 2016 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.
+
+#ifndef MOJO_PUBLIC_CPP_BINDINGS_TESTS_VARIANT_TEST_UTIL_H_
+#define MOJO_PUBLIC_CPP_BINDINGS_TESTS_VARIANT_TEST_UTIL_H_
+
+#include <string.h>
+
+#include "base/logging.h"
+#include "mojo/public/cpp/bindings/interface_request.h"
+
+namespace mojo {
+namespace test {
+
+// Converts a request of Interface1 to a request of Interface0. Interface0 and
+// Interface1 are expected to be two variants of the same mojom interface.
+// In real-world use cases, users shouldn't need to worry about this. Because it
+// is rare to deal with two variants of the same interface in the same app.
+template <typename Interface0, typename Interface1>
+InterfaceRequest<Interface0> ConvertInterfaceRequest(
+    InterfaceRequest<Interface1> request) {
+  DCHECK_EQ(0, strcmp(Interface0::Name_, Interface1::Name_));
+  InterfaceRequest<Interface0> result;
+  result.Bind(request.PassMessagePipe());
+  return result;
+}
+
+}  // namespace test
+}  // namespace mojo
+
+#endif  // MOJO_PUBLIC_CPP_BINDINGS_TESTS_VARIANT_TEST_UTIL_H_
diff --git a/mojo/public/cpp/bindings/tests/wtf_types_unittest.cc b/mojo/public/cpp/bindings/tests/wtf_types_unittest.cc
new file mode 100644
index 0000000..20486eb
--- /dev/null
+++ b/mojo/public/cpp/bindings/tests/wtf_types_unittest.cc
@@ -0,0 +1,134 @@
+// Copyright 2016 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 "base/macros.h"
+#include "base/message_loop/message_loop.h"
+#include "base/run_loop.h"
+#include "mojo/public/cpp/bindings/binding.h"
+#include "mojo/public/cpp/bindings/lib/fixed_buffer.h"
+#include "mojo/public/cpp/bindings/lib/serialization.h"
+#include "mojo/public/cpp/bindings/lib/wtf_serialization.h"
+#include "mojo/public/cpp/bindings/tests/variant_test_util.h"
+#include "mojo/public/interfaces/bindings/tests/test_wtf_types.mojom-blink.h"
+#include "mojo/public/interfaces/bindings/tests/test_wtf_types.mojom.h"
+#include "testing/gtest/include/gtest/gtest.h"
+
+namespace mojo {
+namespace test {
+namespace {
+
+const char kHelloWorld[] = "hello world";
+
+// Replace the "o"s in "hello world" with "o"s with acute.
+const char kUTF8HelloWorld[] = "hell\xC3\xB3 w\xC3\xB3rld";
+
+class TestWTFImpl : public TestWTF {
+ public:
+  explicit TestWTFImpl(TestWTFRequest request)
+      : binding_(this, std::move(request)) {}
+
+  // mojo::test::TestWTF implementation:
+  void EchoString(const String& str,
+                  const EchoStringCallback& callback) override {
+    callback.Run(str);
+  }
+
+ private:
+  Binding<TestWTF> binding_;
+};
+
+class WTFTypesTest : public testing::Test {
+ public:
+  WTFTypesTest() {}
+
+ private:
+  base::MessageLoop loop_;
+};
+
+}  // namespace
+
+TEST_F(WTFTypesTest, WTFToWTFStringSerialization) {
+  Array<WTF::String> strs(4);
+  // strs[0] is null.
+  // strs[1] is empty.
+  strs[1] = "";
+  strs[2] = kHelloWorld;
+  strs[3] = WTF::String::fromUTF8(kUTF8HelloWorld);
+
+  Array<WTF::String> cloned_strs = strs.Clone();
+
+  mojo::internal::SerializationContext context;
+  size_t size = GetSerializedSize_(cloned_strs, &context);
+
+  mojo::internal::FixedBufferForTesting buf(size);
+  mojo::internal::Array_Data<mojo::internal::String_Data*>* data;
+  mojo::internal::ArrayValidateParams validate_params(
+      0, true, new mojo::internal::ArrayValidateParams(0, false, nullptr));
+  SerializeArray_(std::move(cloned_strs), &buf, &data, &validate_params,
+                  &context);
+
+  Array<WTF::String> strs2;
+  Deserialize_(data, &strs2, nullptr);
+
+  EXPECT_TRUE(strs.Equals(strs2));
+}
+
+TEST_F(WTFTypesTest, WTFToMojoStringSerialization) {
+  Array<WTF::String> strs(4);
+  // strs[0] is null.
+  // strs[1] is empty.
+  strs[1] = "";
+  strs[2] = kHelloWorld;
+  strs[3] = WTF::String::fromUTF8(kUTF8HelloWorld);
+
+  Array<WTF::String> cloned_strs = strs.Clone();
+
+  mojo::internal::SerializationContext context;
+  size_t size = GetSerializedSize_(cloned_strs, &context);
+
+  mojo::internal::FixedBufferForTesting buf(size);
+  mojo::internal::Array_Data<mojo::internal::String_Data*>* data;
+  mojo::internal::ArrayValidateParams validate_params(
+      0, true, new mojo::internal::ArrayValidateParams(0, false, nullptr));
+  SerializeArray_(std::move(cloned_strs), &buf, &data, &validate_params,
+                  &context);
+
+  Array<mojo::String> strs2;
+  Deserialize_(data, &strs2, nullptr);
+
+  ASSERT_EQ(4u, strs2.size());
+  EXPECT_TRUE(strs2[0].is_null());
+  EXPECT_TRUE("" == strs2[1]);
+  EXPECT_TRUE(kHelloWorld == strs2[2]);
+  EXPECT_TRUE(kUTF8HelloWorld == strs2[3]);
+}
+
+TEST_F(WTFTypesTest, SendString) {
+  blink::TestWTFPtr ptr;
+  TestWTFImpl impl(ConvertInterfaceRequest<TestWTF>(GetProxy(&ptr)));
+
+  WTF::String strs[4];
+  // strs[0] is null.
+  // strs[1] is empty.
+  strs[1] = "";
+  strs[2] = kHelloWorld;
+  strs[3] = WTF::String::fromUTF8(kUTF8HelloWorld);
+
+  for (size_t i = 0; i < arraysize(strs); ++i) {
+    base::RunLoop loop;
+    // Test that a WTF::String is unchanged after the following conversion:
+    //   - serialized;
+    //   - deserialized as mojo::String;
+    //   - serialized;
+    //   - deserialized as WTF::String.
+    ptr->EchoString(strs[i], [&loop, &strs, &i](const WTF::String& str) {
+      EXPECT_EQ(strs[i], str);
+      loop.Quit();
+    });
+    loop.Run();
+  }
+}
+
+}  // namespace test
+}  // namespace mojo
diff --git a/mojo/public/interfaces/bindings/tests/BUILD.gn b/mojo/public/interfaces/bindings/tests/BUILD.gn
index 464566c..c9b01b4 100644
--- a/mojo/public/interfaces/bindings/tests/BUILD.gn
+++ b/mojo/public/interfaces/bindings/tests/BUILD.gn
@@ -97,3 +97,26 @@ mojom("test_interfaces_blink") {
     ":test_interfaces",
   ]
 }
+
+mojom("test_wtf_types") {
+  testonly = true
+
+  sources = [
+    "test_wtf_types.mojom",
+  ]
+}
+
+mojom("test_wtf_types_blink") {
+  testonly = true
+
+  sources = [
+    "test_wtf_types.mojom",
+  ]
+
+  deps = [
+    ":test_wtf_types",
+  ]
+
+  for_blink = true
+  variant = "blink"
+}
diff --git a/mojo/public/interfaces/bindings/tests/test_wtf_types.mojom b/mojo/public/interfaces/bindings/tests/test_wtf_types.mojom
new file mode 100644
index 0000000..f776309
--- /dev/null
+++ b/mojo/public/interfaces/bindings/tests/test_wtf_types.mojom
@@ -0,0 +1,14 @@
+// Copyright 2016 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.
+
+module mojo.test;
+
+struct TestWTFCodeGeneration {
+  string str;
+  string? nullable_str;
+};
+
+interface TestWTF {
+  EchoString(string? str) => (string? str);
+};
diff --git a/mojo/public/tools/bindings/generators/cpp_templates/interface_declaration.tmpl b/mojo/public/tools/bindings/generators/cpp_templates/interface_declaration.tmpl
index dddbbd3..76888c7 100644
--- a/mojo/public/tools/bindings/generators/cpp_templates/interface_declaration.tmpl
+++ b/mojo/public/tools/bindings/generators/cpp_templates/interface_declaration.tmpl
@@ -53,7 +53,7 @@ class {{interface.name}} {
   }
 {%-     endif %}
 
-  using {{method.name}}Callback = {{interface_macros.declare_callback(method)}};
+  using {{method.name}}Callback = {{interface_macros.declare_callback(method, for_blink)}};
 {%-   endif %}
   virtual void {{method.name}}({{interface_macros.declare_request_params("", method)}}) = 0;
 {%- endfor %}
diff --git a/mojo/public/tools/bindings/generators/cpp_templates/interface_macros.tmpl b/mojo/public/tools/bindings/generators/cpp_templates/interface_macros.tmpl
index b00b1da..f6056e8 100644
--- a/mojo/public/tools/bindings/generators/cpp_templates/interface_macros.tmpl
+++ b/mojo/public/tools/bindings/generators/cpp_templates/interface_macros.tmpl
@@ -5,13 +5,13 @@
 {%-   endfor %}
 {%- endmacro %}
 
-{%- macro declare_callback(method) -%}
+{%- macro declare_callback(method, for_blink) -%}
 mojo::Callback<void(
 {%-   for param in method.response_parameters -%}
 {#- TODO(yzshen): Previously |cpp_result_type| is used here incorrectly.
     The outcome is we will use mojo::String instead of const mojo::String&.
     Preserve the behavior temporarily. #}
-{%- if not param.kind|is_string_kind -%}
+{%- if (not param.kind|is_string_kind) or for_blink -%}
 {{param.kind|cpp_const_wrapper_type}}
 {%- else -%}
 mojo::String
diff --git a/mojo/public/tools/bindings/generators/cpp_templates/module.cc.tmpl b/mojo/public/tools/bindings/generators/cpp_templates/module.cc.tmpl
index 8c9c0fb..4d1dc90 100644
--- a/mojo/public/tools/bindings/generators/cpp_templates/module.cc.tmpl
+++ b/mojo/public/tools/bindings/generators/cpp_templates/module.cc.tmpl
@@ -36,6 +36,10 @@
 #include "mojo/public/cpp/bindings/lib/validation_util.h"
 #include "mojo/public/interfaces/bindings/interface_control_messages.mojom.h"
 
+{%- if for_blink %}
+#include "mojo/public/cpp/bindings/lib/wtf_serialization.h"
+{%- endif %}
+
 {%- for namespace in namespaces_as_array %}
 namespace {{namespace}} {
 {%- endfor %}
diff --git a/mojo/public/tools/bindings/generators/cpp_templates/module.h.tmpl b/mojo/public/tools/bindings/generators/cpp_templates/module.h.tmpl
index af93b84..8046116e 100644
--- a/mojo/public/tools/bindings/generators/cpp_templates/module.h.tmpl
+++ b/mojo/public/tools/bindings/generators/cpp_templates/module.h.tmpl
@@ -32,13 +32,17 @@
 #include "mojo/public/cpp/bindings/map.h"
 #include "mojo/public/cpp/bindings/message_filter.h"
 #include "mojo/public/cpp/bindings/no_interface.h"
-#include "mojo/public/cpp/bindings/string.h"
 #include "mojo/public/cpp/bindings/struct_ptr.h"
 #include "mojo/public/cpp/bindings/struct_traits.h"
 #include "{{variant_path}}-internal.h"
 {%- for import in imports %}
 #include "{{import.module.path}}.h"
 {%- endfor %}
+{%- if not for_blink %}
+#include "mojo/public/cpp/bindings/string.h"
+{%- else %}
+#include "third_party/WebKit/Source/wtf/text/WTFString.h"
+{%- endif %}
 
 {%- for namespace in namespaces_as_array %}
 namespace {{namespace}} {
diff --git a/mojo/public/tools/bindings/generators/mojom_cpp_generator.py b/mojo/public/tools/bindings/generators/mojom_cpp_generator.py
index c2d3a1c..4433740 100644
--- a/mojo/public/tools/bindings/generators/mojom_cpp_generator.py
+++ b/mojo/public/tools/bindings/generators/mojom_cpp_generator.py
@@ -42,9 +42,10 @@ _kind_to_cpp_literal_suffix = {
   mojom.UINT64:       "ULL",
 }
 
-# TODO(rockot): Get rid of this global. This requires some refactoring of the
+# TODO(rockot): Get rid of these globals. This requires some refactoring of the
 # generator library code so that filters can use the generator as context.
 _current_typemap = {}
+_for_blink = False
 
 
 def ConstantValue(constant):
@@ -56,9 +57,10 @@ def DefaultValue(field):
       assert field.default == "default"
       return "%s::New()" % GetNameForKind(field.kind)
     return ExpressionToText(field.default, kind=field.kind)
-  if (mojom.IsStringKind(field.kind) or mojom.IsArrayKind(field.kind) or
-      mojom.IsMapKind(field.kind)):
+  if mojom.IsArrayKind(field.kind) or mojom.IsMapKind(field.kind):
     return "nullptr";
+  if mojom.IsStringKind(field.kind):
+    return "" if _for_blink else "nullptr"
   return ""
 
 def NamespaceToArray(namespace):
@@ -187,7 +189,7 @@ def GetCppArrayArgWrapperType(kind):
     raise Exception("Arrays of associated interface requests not yet "
                     "supported!")
   if mojom.IsStringKind(kind):
-    return "mojo::String"
+    return "WTF::String" if _for_blink else "mojo::String"
   if mojom.IsGenericHandleKind(kind):
     return "mojo::ScopedHandle"
   if mojom.IsDataPipeConsumerKind(kind):
@@ -223,7 +225,7 @@ def GetCppResultWrapperType(kind):
   if mojom.IsAssociatedInterfaceRequestKind(kind):
     return "%sAssociatedRequest" % GetNameForKind(kind.kind)
   if mojom.IsStringKind(kind):
-    return "mojo::String"
+    return "WTF::String" if _for_blink else "mojo::String"
   if mojom.IsGenericHandleKind(kind):
     return "mojo::ScopedHandle"
   if mojom.IsDataPipeConsumerKind(kind):
@@ -265,7 +267,7 @@ def GetCppWrapperType(kind):
   if mojom.IsAssociatedInterfaceRequestKind(kind):
     return "%sAssociatedRequest" % GetNameForKind(kind.kind)
   if mojom.IsStringKind(kind):
-    return "mojo::String"
+    return "WTF::String" if _for_blink else "mojo::String"
   if mojom.IsGenericHandleKind(kind):
     return "mojo::ScopedHandle"
   if mojom.IsDataPipeConsumerKind(kind):
@@ -301,7 +303,7 @@ def GetCppConstWrapperType(kind):
   if mojom.IsEnumKind(kind):
     return GetNameForKind(kind)
   if mojom.IsStringKind(kind):
-    return "const mojo::String&"
+    return "const WTF::String&" if _for_blink else "const mojo::String&"
   if mojom.IsGenericHandleKind(kind):
     return "mojo::ScopedHandle"
   if mojom.IsDataPipeConsumerKind(kind):
@@ -525,6 +527,7 @@ class Generator(generator.Generator):
       "interfaces": self.GetInterfaces(),
       "variant": self.variant,
       "extra_headers": self.GetExtraHeaders(),
+      "for_blink": self.for_blink,
     }
 
   @staticmethod
@@ -550,6 +553,8 @@ class Generator(generator.Generator):
   def GenerateFiles(self, args):
     global _current_typemap
     _current_typemap = self.typemap
+    global _for_blink
+    _for_blink = self.for_blink
     suffix = "-%s" % self.variant if self.variant else ""
     self.Write(self.GenerateModuleHeader(),
         self.MatchMojomFilePath("%s%s.h" % (self.module.name, suffix)))
diff --git a/mojo/public/tools/bindings/mojom.gni b/mojo/public/tools/bindings/mojom.gni
index d8923dd..9ff1af1 100644
--- a/mojo/public/tools/bindings/mojom.gni
+++ b/mojo/public/tools/bindings/mojom.gni
@@ -59,6 +59,9 @@ mojom_generator_sources = [
 #   testonly (optional)
 #
 #   visibility (optional)
+#
+#   for_blink (optional, C++ only)
+#       Use WTF types as generated type for mojo string/array/map.
 template("mojom") {
   assert(
       defined(invoker.sources) || defined(invoker.deps) ||
@@ -158,6 +161,10 @@ template("mojom") {
         }
         inputs += invoker.typemaps
       }
+
+      if (defined(invoker.for_blink) && invoker.for_blink) {
+        args += [ "--for_blink" ]
+      }
     }
   }
 
@@ -245,6 +252,9 @@ template("mojom") {
         full_name = get_label_info(d, "label_no_toolchain")
         deps += [ "${full_name}_${cpp_sources_suffix}" ]
       }
+      if (defined(invoker.for_blink) && invoker.for_blink) {
+        public_deps += [ "//mojo/public/cpp/bindings:wtf_support" ]
+      }
     }
   }
 
diff --git a/mojo/public/tools/bindings/mojom_bindings_generator.py b/mojo/public/tools/bindings/mojom_bindings_generator.py
index 18b9496..130e730 100755
--- a/mojo/public/tools/bindings/mojom_bindings_generator.py
+++ b/mojo/public/tools/bindings/mojom_bindings_generator.py
@@ -143,7 +143,8 @@ class MojomProcessor(object):
       for language, generator_module in generator_modules.iteritems():
         generator = generator_module.Generator(
             module, args.output_dir, typemap=self._typemap.get(language, {}),
-            variant=args.variant, bytecode_path=args.bytecode_path)
+            variant=args.variant, bytecode_path=args.bytecode_path,
+            for_blink=args.for_blink)
         filtered_args = []
         if hasattr(generator_module, 'GENERATOR_PREFIX'):
           prefix = '--' + generator_module.GENERATOR_PREFIX + '_'
@@ -252,6 +253,9 @@ def main():
           "the path from which to load template bytecode; to generate template "
           "bytecode, run %s precompile BYTECODE_PATH" % os.path.basename(
               sys.argv[0])))
+  generate_parser.add_argument("--for_blink", action="store_true",
+                               help="Use WTF types as generated types for mojo "
+                               "string/array/map.")
   generate_parser.set_defaults(func=_Generate)
 
   precompile_parser = subparsers.add_parser("precompile",
diff --git a/mojo/public/tools/bindings/pylib/mojom/generate/generator.py b/mojo/public/tools/bindings/pylib/mojom/generate/generator.py
index 0ecc615..a97d2ea 100644
--- a/mojo/public/tools/bindings/pylib/mojom/generate/generator.py
+++ b/mojo/public/tools/bindings/pylib/mojom/generate/generator.py
@@ -37,12 +37,13 @@ class Generator(object):
   # Pass |output_dir| to emit files to disk. Omit |output_dir| to echo all
   # files to stdout.
   def __init__(self, module, output_dir=None, typemap=None, variant=None,
-               bytecode_path=None):
+               bytecode_path=None, for_blink=False):
     self.module = module
     self.output_dir = output_dir
     self.typemap = typemap or {}
     self.variant = variant
     self.bytecode_path = bytecode_path
+    self.for_blink = for_blink
 
   def GetStructsFromMethods(self):
     result = []
diff --git a/third_party/WebKit/Source/platform/BUILD.gn b/third_party/WebKit/Source/platform/BUILD.gn
index ce0600d..3254fb5 100644
--- a/third_party/WebKit/Source/platform/BUILD.gn
+++ b/third_party/WebKit/Source/platform/BUILD.gn
@@ -542,6 +542,7 @@ test("blink_platform_unittests") {
     "//cc/blink",
     "//mojo/edk/embedder:headers",
     "//mojo/edk/test:test_support",
+    "//mojo/public/cpp/bindings/tests:for_blink_tests",
     "//skia",
     "//testing/gmock",
     "//testing/gtest",
diff --git a/third_party/WebKit/Source/platform/blink_platform_tests.gyp b/third_party/WebKit/Source/platform/blink_platform_tests.gyp
index 7254d69..72a1fb0 100644
--- a/third_party/WebKit/Source/platform/blink_platform_tests.gyp
+++ b/third_party/WebKit/Source/platform/blink_platform_tests.gyp
@@ -76,6 +76,7 @@
         '<(DEPTH)/cc/cc_tests.gyp:cc_test_support',
         '<(DEPTH)/cc/blink/cc_blink.gyp:cc_blink',
         '<(DEPTH)/mojo/mojo_edk.gyp:mojo_common_test_support',
+        '<(DEPTH)/mojo/mojo_edk_tests.gyp:mojo_public_bindings_for_blink_tests',
         '<(DEPTH)/skia/skia.gyp:skia',
         '<(DEPTH)/third_party/harfbuzz-ng/harfbuzz.gyp:harfbuzz-ng',
         '<(DEPTH)/ui/gfx/gfx.gyp:gfx',
diff --git a/third_party/WebKit/Source/wtf/BUILD.gn b/third_party/WebKit/Source/wtf/BUILD.gn
index 9115470..fd3b292 100644
--- a/third_party/WebKit/Source/wtf/BUILD.gn
+++ b/third_party/WebKit/Source/wtf/BUILD.gn
@@ -11,7 +11,10 @@ gypi_values = exec_script("//build/gypi_to_gn.py",
                           "scope",
                           [ "wtf.gypi" ])
 
-visibility = [ "//third_party/WebKit/*" ]
+visibility = [
+  "//mojo/public/cpp/bindings/*",
+  "//third_party/WebKit/*",
+]
 
 config("wtf_config") {
   if (is_win) {