Mojo C++ bindings: make String16 and gfx::Size available in Blink

mojo/common/common_custom_types.mojom

 // 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.common.mojom;
 
 [Native]
 struct FilePath;
 
 [Native]
 struct ListValue;
 
 [Native]
 struct DictionaryValue;
 
 [Native]
 struct Time;
 
 struct TimeDelta {
   int64 microseconds;
 };
 
 [Native]
 struct TimeTicks;
 
-[Native]
-struct String16;
+// Corresponds to |base::string16| in base/strings/string16.h
+// Corresponds to |blink::WebString| in

[Tom Sepez, 2016/09/29 20:13:08]

Wouldn't this violate DEPS, in some sense; I didn't think /mojo was allowed to
know about blink (base OK since mojom built on base).

[Zhiqiang Zhang (Slow), 2016/09/29 20:39:31]

There some other types which has been mapped to blink structures, such as:
String->WTF::String
Array->WTF::Vector

In general, my purpose is to send structures from WebKit/Source to chromium
directly, so we could avoid having a layer in content/renderer to do the type
conversion.

There's another example, which maps mojo Url to blink::KURL. See "KURL.typemap"

I think the *.mojom-blink.* bindings are only used in Blink, which serializes
Blink structures for mojo communication, so it's probably OK?

Maybe rockot@ has better answer.

[Ken Rockot(use gerrit already), 2016/09/29 22:00:48]

This is fine. The typemap which actually imposes DEPS is defined in
third_party/WebKit and only used by third_party/WebKit code.

It's a little weird to reference blink types even in comments, but I think it's
OK in this case, for clarity.

+// third_party/WebKit/public/platform/WebString.h, and only accept non-null
+// |blink::WebString|.
+struct String16 {
+  array<uint16> data;
+};
 
 // Corresponds to |base::UnguessableToken| in base/unguessable_token.h
 struct UnguessableToken {
   uint64 high;
   uint64 low;
 };
 
 // Corresponds to |base::Version| in base/version.h
 struct Version {
   array<uint32> components;
 };