Ignore MISSING_VIA_HEADER_OTHER bypasses if in relevant finch trial

For clients that are part of the finch trial, change the proxy bypass
logic to not trigger a proxy bypass when a response with a non-4xx
response code is expected to have the data reduction proxy header, but
the data reduction proxy via header is missing.

BUG=413035

Review URL: https://codereview.chromium.org/583363002

Cr-Commit-Position: refs/heads/master@{#295825}

components/data_reduction_proxy/browser/data_reduction_proxy_params.cc

@@ -66,6 +66,19 @@ bool DataReductionProxyParams::IsIncludedInCriticalPathBypassFieldTrial() {
           "DataCompressionProxyCriticalBypass") == kEnabled;
 }
 
+// static
+bool DataReductionProxyParams::IsIncludedInHoldbackFieldTrial() {
+  return FieldTrialList::FindFullName(
+      "DataCompressionProxyHoldback") == kEnabled;
+}
+
+// static
+bool DataReductionProxyParams::
+    IsIncludedInRemoveMissingViaHeaderOtherBypassFieldTrial() {
+  return FieldTrialList::FindFullName(
+      "DataReductionProxyRemoveMissingViaHeaderOtherBypass") == kEnabled;
+}
+
 DataReductionProxyTypeInfo::DataReductionProxyTypeInfo()
     : proxy_servers(),
       is_fallback(false),
@@ -76,11 +89,6 @@ DataReductionProxyTypeInfo::DataReductionProxyTypeInfo()
 DataReductionProxyTypeInfo::~DataReductionProxyTypeInfo(){
 }
 
-bool DataReductionProxyParams::IsIncludedInHoldbackFieldTrial() {
-  return FieldTrialList::FindFullName(
-      "DataCompressionProxyHoldback") == kEnabled;
-}
-
 DataReductionProxyParams::DataReductionProxyParams(int flags)
     : allowed_((flags & kAllowed) == kAllowed),
       fallback_allowed_((flags & kFallbackAllowed) == kFallbackAllowed),

components/data_reduction_proxy/browser/data_reduction_proxy_params.h

@@ -83,6 +83,13 @@ class DataReductionProxyParams {
   // is in effect.
   static bool IsIncludedInHoldbackFieldTrial();
 
+  // Returns true if this client is part of a field trial that removes the
+  // |MISSING_VIA_HEADER_OTHER| proxy bypass case. This experiment changes proxy
+  // bypass logic to not trigger a proxy bypass when a response with a non-4xx
+  // response code is expected to have a data reduction proxy via header, but
+  // the data reduction proxy via header is missing.
+  static bool IsIncludedInRemoveMissingViaHeaderOtherBypassFieldTrial();
+
   // Constructs configuration parameters. If |kAllowed|, then the standard
   // data reduction proxy configuration is allowed to be used. If
   // |kfallbackAllowed| a fallback proxy can be used if the primary proxy is

components/data_reduction_proxy/browser/data_reduction_proxy_protocol.cc

@@ -73,6 +73,15 @@ bool MaybeBypassProxyAndPrepareToRetry(
   DataReductionProxyBypassType bypass_type =
       GetDataReductionProxyBypassType(original_response_headers,
                                       &data_reduction_proxy_info);
+
+  if (bypass_type == BYPASS_EVENT_TYPE_MISSING_VIA_HEADER_OTHER &&
+      DataReductionProxyParams::
+          IsIncludedInRemoveMissingViaHeaderOtherBypassFieldTrial()) {
+    // Ignore MISSING_VIA_HEADER_OTHER proxy bypass events if the client is part
+    // of the field trial to remove these kinds of bypasses.
+    bypass_type = BYPASS_EVENT_TYPE_MAX;
+  }
+
   if (proxy_bypass_type)
     *proxy_bypass_type = bypass_type;
   if (bypass_type == BYPASS_EVENT_TYPE_MAX)