site-per-process is the default on desktop even without of field trials.

This CL flips the default value of features::kSitePerProcess on desktop
to base::FEATURE_ENABLED_BY_DEFAULT.

Bug: 874998
Change-Id: Ia1a999072e87cc32fbde1bb70f8bb39e9b3053a7
Reviewed-on: https://chromium-review.googlesource.com/1178622Reviewed-by: Steven Holte <holte@chromium.org>
Reviewed-by: Alex Moshchuk <alexmos@chromium.org>
Commit-Queue: Łukasz Anforowicz <lukasza@chromium.org>
Cr-Commit-Position: refs/heads/master@{#584254}

chrome/common/chrome_features.cc

@@ -512,8 +512,14 @@ const base::Feature kShowTrustedPublisherURL{"ShowTrustedPublisherURL",
 // Launch bug: https://crbug.com/739418.  This is a //chrome-layer feature to
 // avoid turning on site-per-process by default for *all* //content embedders
 // (e.g. this approach lets ChromeCast avoid site-per-process mode).
-const base::Feature kSitePerProcess{"site-per-process",
-                                    base::FEATURE_DISABLED_BY_DEFAULT};
+const base::Feature kSitePerProcess {
+  "site-per-process",
+#if defined(OS_ANDROID)
+      base::FEATURE_DISABLED_BY_DEFAULT
+#else
+      base::FEATURE_ENABLED_BY_DEFAULT
+#endif
+};
 
 // kSitePerProcessOnlyForHighMemoryClients is checked before kSitePerProcess,
 // and (if enabled) can restrict if kSitePerProcess feature is checked at all -

testing/variations/fieldtrial_testing_config.json

@@ -4088,24 +4088,6 @@
             ]
         }
     ],
-    "SitePerProcess": [
-        {
-            "platforms": [
-                "chromeos",
-                "linux",
-                "windows",
-                "mac"
-            ],
-            "experiments": [
-                {
-                    "name": "SitePerProcess_Enabled",
-                    "enable_features": [
-                        "site-per-process"
-                    ]
-                }
-            ]
-        }
-    ],
     "SocketReadIfReady": [
         {
             "platforms": [