Make chrome sync response compression as default

BUG=509728

Review-Url: https://codereview.chromium.org/2046493007
Cr-Commit-Position: refs/heads/master@{#398730}

sync/BUILD.gn

@@ -725,7 +725,6 @@ test("sync_unit_tests") {
     "//testing/gtest",
     "//third_party/leveldatabase",
     "//third_party/protobuf:protobuf_lite",
-    "//third_party/zlib",
   ]
 
   if (is_chromeos) {

sync/internal_api/http_bridge.cc

@@ -12,12 +12,10 @@
 #include "base/bit_cast.h"
 #include "base/location.h"
 #include "base/message_loop/message_loop.h"
-#include "base/metrics/field_trial.h"
 #include "base/metrics/histogram_macros.h"
 #include "base/metrics/sparse_histogram.h"
 #include "base/single_thread_task_runner.h"
 #include "base/strings/string_number_conversions.h"
-#include "base/strings/string_util.h"
 #include "base/strings/stringprintf.h"
 #include "base/threading/thread_task_runner_handle.h"
 #include "net/base/load_flags.h"
@@ -47,12 +45,6 @@ void LogTimeout(bool timed_out) {
   UMA_HISTOGRAM_BOOLEAN("Sync.URLFetchTimedOut", timed_out);
 }
 
-bool IsSyncHttpContentCompressionEnabled() {
-  const std::string group_name =
-      base::FieldTrialList::FindFullName("SyncHttpContentCompression");
-  return StartsWith(group_name, "Enabled", base::CompareCase::SENSITIVE);
-}
-
 void RecordSyncRequestContentLengthHistograms(int64_t compressed_content_length,
                                               int64_t original_content_length) {
   UMA_HISTOGRAM_COUNTS("Sync.RequestContentLength.Compressed",
@@ -253,13 +245,6 @@ void HttpBridge::MakeAsynchronousPost() {
   fetch_state_.url_poster->SetRequestContext(request_context_getter_.get());
   fetch_state_.url_poster->SetExtraRequestHeaders(extra_headers_);
 
-  if (!IsSyncHttpContentCompressionEnabled()) {
-    // We set "accept-encoding" here to avoid URLRequestHttpJob adding "gzip"
-    // into "accept-encoding" later.
-    fetch_state_.url_poster->AddExtraRequestHeader(base::StringPrintf(
-        "%s: %s", net::HttpRequestHeaders::kAcceptEncoding, "deflate"));
-  }
-
   fetch_state_.url_poster->SetUploadData(content_type_, request_content_);
   RecordSyncRequestContentLengthHistograms(request_content_.size(),
                                            request_content_.size());

sync/internal_api/http_bridge_unittest.cc

@@ -6,10 +6,8 @@
 #include <stdint.h>
 
 #include "base/bit_cast.h"
-#include "base/metrics/field_trial.h"
 #include "base/strings/stringprintf.h"
 #include "base/synchronization/waitable_event.h"
-#include "base/test/mock_entropy_provider.h"
 #include "base/threading/thread.h"
 #include "build/build_config.h"
 #include "net/http/http_response_headers.h"
@@ -21,7 +19,6 @@
 #include "sync/internal_api/public/http_bridge.h"
 #include "sync/internal_api/public/http_post_provider_factory.h"
 #include "testing/gtest/include/gtest/gtest.h"
-#include "third_party/zlib/zlib.h"
 
 namespace syncer {
 
@@ -270,9 +267,6 @@ TEST_F(MAYBE_SyncHttpBridgeTest, CompressedRequestHeaderCheck) {
 
   int os_error = 0;
   int response_code = 0;
-  base::FieldTrialList field_trial_list(new base::MockEntropyProvider());
-  base::FieldTrialList::CreateFieldTrial("SyncHttpContentCompression",
-                                         "Enabled");
   bool success = http_bridge->MakeSynchronousPost(&os_error, &response_code);
   EXPECT_TRUE(success);
   EXPECT_EQ(200, response_code);
@@ -312,10 +306,6 @@ TEST_F(MAYBE_SyncHttpBridgeTest, TestMakeSynchronousPostLiveComprehensive) {
   std::string response(http_bridge->GetResponseContent(),
                        http_bridge->GetResponseContentLength());
   EXPECT_EQ(std::string::npos, response.find("Cookie:"));
-  EXPECT_NE(std::string::npos,
-            response.find(base::StringPrintf(
-                "%s: %s", net::HttpRequestHeaders::kAcceptEncoding,
-                "deflate")));
   EXPECT_NE(std::string::npos,
             response.find(base::StringPrintf("%s: %s",
                           net::HttpRequestHeaders::kUserAgent, kUserAgent)));