Do not allow CORS responses to "same-origin" requests

This matches the change in the Fetch spec:
whatwg/fetch#629

This CL also removes the UseCounter for cross-origin CORS responses to
same-origin requests because it will be unreachable after hereafter.

Chrome status: https://www.chromestatus.com/feature/5694278818856960

Bug: 800234, 784018
Change-Id: Id843a302fa5d0614de1c3ef1c0a39bcf92f7e3ef
Reviewed-on: https://chromium-review.googlesource.com/866849
Reviewed-by: Matt Falkenhagen <falken@chromium.org>
Reviewed-by: Tsuyoshi Horo <horo@chromium.org>
Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Commit-Queue: Yannic Bonenberger <contact@yannic-bonenberger.com>
Cr-Original-Commit-Position: refs/heads/master@{#531594}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: 2e1f3c3724269c16527397f488530cd68003bf16

metrics/histograms/enums.xml

@@ -17573,7 +17573,8 @@ Called by update_net_error_codes.py.-->
   <int value="2228" label="DocumentPageShowRegistered"/>
   <int value="2229" label="DocumentPageShowFired"/>
   <int value="2230" label="ReplaceCharsetInXHR"/>
-  <int value="2231" label="RespondToSameOriginRequestWithCrossOriginResponse"/>
+  <int value="2231"
+      label="RespondToSameOriginRequestWithCrossOriginResponse (obsolete)"/>
   <int value="2232" label="LinkRelModulePreload"/>
   <int value="2233" label="PerformanceMeasurePassedInObject"/>
   <int value="2234" label="PerformanceMeasurePassedInNavigationTiming"/>
@@ -38825,6 +38826,7 @@ Called by update_net_trust_anchors.py.-->
   <int value="13" label="ForeignFetchMismatchedOrigin"/>
   <int value="14" label="RedirectedResponseForNotFollowRequest"/>
   <int value="15" label="DataPipeCreationFailed (insufficient resources)"/>
+  <int value="16" label="ResponseTypeCORSForRequestModeSameOrigin"/>
 </enum>
 
 <enum name="ServiceWorkerSite">