Revert of Remove support for Alt-Svc/Alternate Protocol Probability (patchset #8 id:140001 of https://codereview.chromium.org/1699653002/ )

Reason for revert:
https://bugs.chromium.org/p/chromium/issues/detail?id=594921

Basically parts of http_stream_factory_impl_unittest.cc are only compiled if ENABLE_BIDIRECTIONAL_STREAM is a build flag and you haven't updated these parts of the file.

Original issue's description:
> Remove support forAlt-Svc/Alternate Protocol Probability
>
> Committed: https://crrev.com/dced4c771d25317d26a0f6e258c7b7f64d4e8eea
> Cr-Commit-Position: refs/heads/master@{#379652}
>
> Committed: https://crrev.com/740688bec5c66af00debe117b6d375ecd212e570
> Cr-Commit-Position: refs/heads/master@{#381134}

TBR=bnc@chromium.org,eroman@chromium.org,mef@chromium.org,rch@chromium.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true

Review URL: https://codereview.chromium.org/1802893002

Cr-Commit-Position: refs/heads/master@{#381197}

5 files changed, 41 insertions, 0 deletions

diff --git a/ios/crnet/CrNet.h b/ios/crnet/CrNet.h
index 043ee6e..2fbb48f2 100644
--- a/ios/crnet/CrNet.h
+++ b/ios/crnet/CrNet.h
@@ -35,6 +35,29 @@ typedef void(^ClearCacheCallback)(int errorCode);
 + (void)setSDCHEnabled:(BOOL)sdchEnabled
          withPrefStore:(NSString*)filename;
 
+// Set the alternate protocol threshold. Servers announce alternate protocols
+// with a probability value; any alternate protocol whose probability value is
+// greater than this value will be used, so |alternateProtocolThreshold| == 0
+// implies any announced alternate protocol will be used, and
+// |alternateProtocolThreshold| == 1 implies no alternate protocol will ever be
+// used. Note that individual alternate protocols must also be individually
+// enabled to be considered; currently the only alternate protocol is QUIC (SPDY
+// is not controlled by this mechanism).
+//
+// For example, imagine your service has two frontends a.service.com and
+// b.service.com, and you would like to divide your users into three classes:
+//   Users who use QUIC for both a and b
+//   Users who use QUIC for a but not b
+//   Users who use QUIC for neither a nor b
+// You can achieve that effect with:
+//   a.service.com advertises QUIC with p=0.67
+//   b.service.com advertises QUIC with p=0.33
+//   alternateProtocolThreshold set to a uniform random number in [0,1]
+// Now equal proportions of users will fall into the three experimental groups.
+//
+// The default for this value is 1.0, i.e. all alternate protocols disabled.
++ (void)setAlternateProtocolThreshold:(double)alternateProtocolThreshold;
+
 // |userAgent| is expected to be of the form Product/Version.
 // Example: Foo/3.0.0.0
 //
diff --git a/ios/crnet/CrNet.mm b/ios/crnet/CrNet.mm
index 0347344..2c91094 100644
--- a/ios/crnet/CrNet.mm
+++ b/ios/crnet/CrNet.mm
@@ -16,6 +16,7 @@ static BOOL g_quic_enabled = NO;
 static BOOL g_sdch_enabled = NO;
 static NSString* g_user_agent = nil;
 static NSString* g_sdch_pref_store_filename = nil;
+static double g_alternate_protocol_threshold = 1.0;
 static RequestFilterBlock g_request_filter_block = nil;
 
 @implementation CrNet
@@ -38,6 +39,10 @@ static RequestFilterBlock g_request_filter_block = nil;
   g_user_agent = userAgent;
 }
 
++ (void)setAlternateProtocolThreshold:(double)alternateProtocolThreshold {
+  g_alternate_protocol_threshold = alternateProtocolThreshold;
+}
+
 + (void)installInternal {
   CrNetEnvironment::Initialize();
   std::string partial_user_agent = base::SysNSStringToUTF8(g_user_agent);
@@ -50,6 +55,8 @@ static RequestFilterBlock g_request_filter_block = nil;
     std::string filename = base::SysNSStringToUTF8(g_sdch_pref_store_filename);
     g_chrome_net->set_sdch_pref_store_filename(filename);
   }
+  g_chrome_net->set_alternate_protocol_threshold(
+      g_alternate_protocol_threshold);
 
   g_chrome_net->Install();
   g_chrome_net->SetHTTPProtocolHandlerRegistered(true);
diff --git a/ios/crnet/crnet_consumer/crnet_consumer_app_delegate.mm b/ios/crnet/crnet_consumer/crnet_consumer_app_delegate.mm
index b224eda..ca44848 100644
--- a/ios/crnet/crnet_consumer/crnet_consumer_app_delegate.mm
+++ b/ios/crnet/crnet_consumer/crnet_consumer_app_delegate.mm
@@ -45,6 +45,8 @@
     didFinishLaunchingWithOptions:(NSDictionary*)launchOptions {
   [CrNet setPartialUserAgent:@"Dummy/1.0"];
   [CrNet setQuicEnabled:YES];
+  // Always use QUIC if able.
+  [CrNet setAlternateProtocolThreshold:0.0];
   [CrNet setSDCHEnabled:YES withPrefStore:[self SDCHPrefStoreFileName]];
   [CrNet install];
   [CrNet startNetLogToFile:[self currentNetLogFileName] logBytes:NO];
diff --git a/ios/crnet/crnet_environment.h b/ios/crnet/crnet_environment.h
index 5a698897..a0b49c1 100644
--- a/ios/crnet/crnet_environment.h
+++ b/ios/crnet/crnet_environment.h
@@ -93,10 +93,16 @@ class CrNetEnvironment {
   void set_sdch_pref_store_filename(const std::string& pref_store) {
     sdch_pref_store_filename_ = pref_store;
   }
+  void set_alternate_protocol_threshold(double threshold) {
+    alternate_protocol_threshold_ = threshold;
+  }
 
   bool spdy_enabled() const { return spdy_enabled_; }
   bool quic_enabled() const { return quic_enabled_; }
   bool sdch_enabled() const { return sdch_enabled_; }
+  double alternate_protocol_threshold() const {
+    return alternate_protocol_threshold_;
+  }
 
   // Clears the network stack's disk cache.
   void ClearCache(ClearCacheCallback callback);
@@ -136,6 +142,7 @@ class CrNetEnvironment {
   bool quic_enabled_;
   bool sdch_enabled_;
   std::string sdch_pref_store_filename_;
+  double alternate_protocol_threshold_;
 
   static CrNetEnvironment* chrome_net_;
   scoped_ptr<base::Thread> network_io_thread_;
diff --git a/ios/crnet/crnet_environment.mm b/ios/crnet/crnet_environment.mm
index 4b75a5a..128d76b 100644
--- a/ios/crnet/crnet_environment.mm
+++ b/ios/crnet/crnet_environment.mm
@@ -445,6 +445,8 @@ void CrNetEnvironment::InitializeOnNetworkThread() {
   params.enable_http2 = spdy_enabled();
   params.parse_alternative_services = false;
   params.enable_quic = quic_enabled();
+  params.alternative_service_probability_threshold =
+      alternate_protocol_threshold_;
 
   if (!params.channel_id_service) {
     // The main context may not have a ChannelIDService, since it is lazily