Revert of Remove support for Alt-Svc/Alternate Protocol Probability (patchset #7 id:120001 of https://codereview.chromium.org/1699653002/ )

Reason for revert:
This appears to have broken the following bot: https://build.chromium.org/p/chromium.mac/builders/iOS_Device_%28ninja%29/builds/43364

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

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/1773853003

Cr-Commit-Position: refs/heads/master@{#379658}

1 files changed, 6 insertions, 0 deletions

diff --git a/chrome/common/chrome_switches.cc b/chrome/common/chrome_switches.cc
index d32a32f3..b1be5b9 100644
--- a/chrome/common/chrome_switches.cc
+++ b/chrome/common/chrome_switches.cc
@@ -66,6 +66,12 @@ const char kAllowOutdatedPlugins[]          = "allow-outdated-plugins";
 // URLs. This provides an override to get the old insecure behavior.
 const char kAllowRunningInsecureContent[]   = "allow-running-insecure-content";
 
+// Specifies the probability threshold for alternative services: an advertised
+// alternative service will only be honored if the advertised probability is
+// greater than or equal to this threshold.
+const char kAlternativeServiceProbabilityThreshold[] =
+    "alternative-service-probability-threshold";
+
 // Prevents Chrome from requiring authorization to run certain widely installed
 // but less commonly used plugins.
 const char kAlwaysAuthorizePlugins[]        = "always-authorize-plugins";