Teach WebURLRequest about Fetch's "frame type" concept.

public/platform/WebURLRequest.h

Index: public/platform/WebURLRequest.h
diff --git a/public/platform/WebURLRequest.h b/public/platform/WebURLRequest.h
index edb43a884d9ab7454a2938b1bb3244a9e5c31fc1..e3842bcce9d0d03a45fa8db82a4364eb69e66aa2 100644
--- a/public/platform/WebURLRequest.h
+++ b/public/platform/WebURLRequest.h
@@ -88,6 +88,8 @@ public:
         TargetIsUnspecified = 17,
     };
 
+    // Corresponds to Fetch's "context": http://fetch.spec.whatwg.org/#concept-request-context
+    //
     // FIXME: Drop the TargetType enum once embedders are updated upstream.
     enum RequestContext {
         RequestContextUnspecified = 0,
@@ -124,6 +126,14 @@ public:
         RequestContextXSLT
     };
 
+    // Corresponds to Fetch's "context frame type": http://fetch.spec.whatwg.org/#concept-request-context-frame-type
+    enum FrameType {
+        FrameTypeAuxiliary,
+        FrameTypeNested,
+        FrameTypeNone,
+        FrameTypeTopLevel
+    };
+
     class ExtraData {
     public:
         virtual ~ExtraData() { }
@@ -197,6 +207,9 @@ public:
     BLINK_PLATFORM_EXPORT RequestContext requestContext() const;
     BLINK_PLATFORM_EXPORT void setRequestContext(RequestContext);
 
+    BLINK_PLATFORM_EXPORT FrameType frameType() const;
+    BLINK_PLATFORM_EXPORT void setFrameType(FrameType);
+
     BLINK_PLATFORM_EXPORT WebReferrerPolicy referrerPolicy() const;
 
     // Adds an HTTP origin header if it is empty and the HTTP method of the