Enable DoH by default in code

The "DnsOverHttps" feature along with the "ShowUi" param is approved for
launch and will soon be launched to 100% for win/mac/cros/android, so
enable the feature/param by default for those platforms.

There shouldn't be anything left with the feature enabled but the ShowUi
param disabled, but I'm still switching the param on platform because I
don't understand the UI code enough to be sure nothing in there will
only check the param without the feature and not accidentally enable the
UI.  I'll figure that out and handle it later in a more thorough cleanup
to fully delete the ShowUi param.

Also note that it is traditional to delete the fieldtrial testing config
entries when changing experiments to be enabled by default, but I'm
leaving it in place here because it is covering testing of the
"DisabledProviders" param that is not yet launching to a final state.

Bug: 878582,1098039
Change-Id: I57bb6264047b7ed426bf57fca9f6301f71312ba2
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2429243
Commit-Queue: Eric Orth <ericorth@chromium.org>
Commit-Queue: Dan McArdle <dmcardle@chromium.org>
Auto-Submit: Eric Orth <ericorth@chromium.org>
Reviewed-by: Dan McArdle <dmcardle@chromium.org>
Cr-Commit-Position: refs/heads/master@{#810308}

chrome/common/chrome_features.cc

@@ -269,8 +269,15 @@ const base::Feature kDesktopPWAsWithoutExtensions{
     "DesktopPWAsWithoutExtensions", base::FEATURE_ENABLED_BY_DEFAULT};
 
 // Enable DNS over HTTPS (DoH).
-const base::Feature kDnsOverHttps{"DnsOverHttps",
-                                  base::FEATURE_DISABLED_BY_DEFAULT};
+const base::Feature kDnsOverHttps {
+  "DnsOverHttps",
+#if defined(OS_WIN) || defined(OS_CHROMEOS) || defined(OS_MAC) || \
+    defined(OS_ANDROID)
+      base::FEATURE_ENABLED_BY_DEFAULT
+#else
+      base::FEATURE_DISABLED_BY_DEFAULT
+#endif
+};
 
 // Provides a mechanism to remove providers from the dropdown list in the
 // settings UI. Separate multiple provider ids with commas. See the
@@ -284,8 +291,15 @@ const base::FeatureParam<bool> kDnsOverHttpsFallbackParam{&kDnsOverHttps,
                                                           "Fallback", true};
 
 // Sets whether the DoH setting is displayed in the settings UI.
-const base::FeatureParam<bool> kDnsOverHttpsShowUiParam{&kDnsOverHttps,
-                                                        "ShowUi", false};
+const base::FeatureParam<bool> kDnsOverHttpsShowUiParam {
+  &kDnsOverHttps, "ShowUi",
+#if defined(OS_WIN) || defined(OS_CHROMEOS) || defined(OS_MAC) || \
+    defined(OS_ANDROID)
+      true
+#else
+      false
+#endif
+};
 
 // Supply one or more space-separated DoH server URI templates to use when this
 // feature is enabled. If no templates are specified, then a hardcoded mapping