[Presentation API] 1-UA presentation support + presenter APIs.

content/browser/presentation/presentation_type_converters.h

Index: content/browser/presentation/presentation_type_converters.h
diff --git a/content/browser/presentation/presentation_type_converters.h b/content/browser/presentation/presentation_type_converters.h
index f66c3230aba0baffd31ff555ef897b8ddeea7d84..0d3fb2f445772297b97818f30c9032e461119b72 100644
--- a/content/browser/presentation/presentation_type_converters.h
+++ b/content/browser/presentation/presentation_type_converters.h
@@ -28,7 +28,8 @@ struct TypeConverter<presentation::PresentationSessionInfoPtr,
       const content::PresentationSessionInfo& input) {
     presentation::PresentationSessionInfoPtr output(
         presentation::PresentationSessionInfo::New());
-    output->url = input.presentation_url;
+    if (!input.presentation_url.empty())

[mark a. foltz, 2015/10/12 21:56:10]

What is creating a presentation with an empty URL?

[whywhat, 2015/10/13 15:21:31]

the default value of output->url is empty anyway, what's wrong with assigning an
empty url to it?

[imcheng, 2015/10/17 01:00:24]

PresentationConnection objects in receiving contexts have undefined presentation
URL according to the spec.

[imcheng, 2015/10/17 01:00:24]

I believe it makes a difference in mojo. mojo::String are initially considered
"null". When you assign to it with a std::string, it becomes non-null. So for
mojo::String, there is a difference between a "null" empty and a non-null empty.
I was trying to use nulls for the url field in content/ code but it turns out to
be confusing anyways, so I will just check for empty instead.

+      output->url = input.presentation_url;
     output->id = input.presentation_id;
     return output.Pass();
   }