Implement "scope" Web Manifest parsing

content/public/common/manifest.h

Index: content/public/common/manifest.h
diff --git a/content/public/common/manifest.h b/content/public/common/manifest.h
index 8cc19da99ac0a047da589a3ce617f6a15fdedc5a..2a9e35c7e2fc164d06b01018e6f7534201d8c318 100644
--- a/content/public/common/manifest.h
+++ b/content/public/common/manifest.h
@@ -126,6 +126,9 @@ struct CONTENT_EXPORT Manifest {
   // Null if parsing failed or the field was not present.
   base::NullableString16 gcm_sender_id;
 
+  // Empty if the parsing failed or the field was not present.
+  GURL scope;
+
   // Maximum length for all the strings inside the Manifest when it is sent over
   // IPC. The renderer process should truncate the strings before sending the
   // Manifest and the browser process must do the same when receiving it.