fetch: Remove the now-unneeded TrustTokens.FetchFailedReason enum

crrev.com/c/2442229 added some temporary histogramming to FetchManager to identify why failing Trust Tokens operations were failing. Now that
we've found the cause (crbug.com/1128174; internal due to internal repro instructions, sorry), we can remove this instrumentation and clear up a hundred lines or so in fetch_manager.cc. We're keeping
Net.TrustTokens.NetErrorForTrustTokenOperation, which we added at close to the same time, around to use a health indicator.

Change-Id: Ib7178d30a03b1aaa529aafdd4c9f36cfc84e1dbc
Fixed: 1133944
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2561778
Commit-Queue: David Van Cleve <davidvc@chromium.org>
Reviewed-by: Yutaka Hirano <yhirano@chromium.org>
Reviewed-by: Charlie Harrison <csharrison@chromium.org>
Cr-Commit-Position: refs/heads/master@{#832069}

content/test/trust_token_browsertest.cc

@@ -39,7 +39,6 @@
 #include "services/network/trust_tokens/test/trust_token_test_util.h"
 #include "testing/gmock/include/gmock/gmock.h"
 #include "testing/gtest/include/gtest/gtest.h"
-#include "third_party/blink/public/platform/resource_request_blocked_reason.h"
 #include "url/gurl.h"
 #include "url/origin.h"
 #include "url/url_canon_stdstring.h"
@@ -546,7 +545,7 @@ IN_PROC_BROWSER_TEST_F(TrustTokenBrowsertest, RecordsNetErrorCodes) {
 }
 
 IN_PROC_BROWSER_TEST_F(TrustTokenBrowsertest, RecordsFetchFailureReasons) {
-  // Verify that the Net.TrustTokens.FetchFailedReason.* metrics
+  // Verify that the Net.TrustTokens.NetErrorForFetchFailure.* metrics
   // record successfully by testing one case with a blocked resource, one case
   // with a generic net-stack failure, and one case with a Trust Tokens
   // operation failure.
@@ -568,10 +567,6 @@ IN_PROC_BROWSER_TEST_F(TrustTokenBrowsertest, RecordsFetchFailureReasons) {
                                    .catch(err => err.name);)"));
 
   content::FetchHistogramsFromChildProcesses();
-  histograms.ExpectUniqueSample(
-      "Net.TrustTokens.FetchFailedReason.Issuance",
-      9 /* fetch_manager.cc::FailedReason::kOtherNonBlockReason */,
-      /*expected_count=*/1);
   histograms.ExpectUniqueSample(
       "Net.TrustTokens.NetErrorForFetchFailure.Issuance", net::ERR_FAILED,
       /*expected_count=*/1);
@@ -585,10 +580,6 @@ IN_PROC_BROWSER_TEST_F(TrustTokenBrowsertest, RecordsFetchFailureReasons) {
                    .catch(err => err.name);)"));
 
   content::FetchHistogramsFromChildProcesses();
-  histograms.ExpectUniqueSample(
-      "Net.TrustTokens.FetchFailedReason.Redemption",
-      8 /* fetch_manager.cc::FailedReason::kTrustTokensError */,
-      /*expected_count=*/1);
   histograms.ExpectUniqueSample(
       "Net.TrustTokens.NetErrorForFetchFailure.Redemption",
       net::ERR_TRUST_TOKEN_OPERATION_FAILED,
@@ -613,12 +604,6 @@ IN_PROC_BROWSER_TEST_F(TrustTokenBrowsertest, RecordsFetchFailureReasons) {
               HasSubstr("Failed to fetch"));
 
   content::FetchHistogramsFromChildProcesses();
-  histograms.ExpectBucketCount(
-      "Net.TrustTokens.FetchFailedReason.Issuance",
-      // fetch_manager.cc::FailedReason::
-      // kCorpNotSameOriginAfterDefaultedToSameOriginByCoep
-      21,
-      /*expected_count=*/1);
   histograms.ExpectBucketCount(
       "Net.TrustTokens.NetErrorForFetchFailure.Issuance",
       net::ERR_BLOCKED_BY_RESPONSE,

tools/metrics/histograms/histograms_xml/net/histograms.xml

@@ -4829,6 +4829,9 @@ reviews. Googlers can read more about this at go/gwsq-gerrit.
 <histogram base="true" name="Net.TrustTokens.FetchFailedReason"
     enum="FetchFailedReasonOrResourceRequestBlockedReason"
     expires_after="2021-03-30">
+  <obsolete>
+    This was a temporary addition used for debugging during M88.
+  </obsolete>
 <!-- Name completed by histogram_suffixes name="TrustTokenOperationType" -->
 
   <owner>davidvc@chromium.org</owner>
@@ -4850,8 +4853,9 @@ reviews. Googlers can read more about this at go/gwsq-gerrit.
   <owner>privacy-sandbox-dev@chromium.org</owner>
   <summary>
     The net error for a failed Fetch API call with an associated Trust Tokens
-    operation. This might help debug a surfeit of 'TypeError: failed to fetch'
-    observed in live testing.
+    operation. This was originally added to help debug a surfeit of 'TypeError:
+    failed to fetch' observed in live testing, and it is now retained since it's
+    useful for ongoing health monitoring.
   </summary>
 </histogram>