Add doc comment that url::Origin::Create may change the scheme.

Fixed: 1054974
Change-Id: Ica1b44284e99f9b56f49bcbb602bfd0cdb6de648
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2081263Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Commit-Queue: Daniel Cheng <dcheng@chromium.org>
Cr-Commit-Position: refs/heads/master@{#746632}

url/origin.h

@@ -145,6 +145,9 @@ class COMPONENT_EXPORT(URL) Origin {
   // 2. 'filesystem' URLs behave as 'blob' URLs (that is, the origin is parsed
   //    out of everything in the URL which follows the scheme).
   // 3. 'file' URLs all parse as ("file", "", 0).
+  //
+  // Note that the returned Origin may have a different scheme and host from
+  // |url| (e.g. in case of blob URLs - see OriginTest.ConstructFromGURL).
   static Origin Create(const GURL& url);
 
   // Creates an Origin for the resource |url| as if it were requested