Add UsePdfCompositorServiceForTest for fieldtrial testing

Add "UsePdfCompositorServiceForTest" experiment to the field trial under
tests for all desktop platforms. It tests the new PDF generation service
which supports OOPIF printing.

BUG=824867

Change-Id: I808c8ed04509e5d6a6074d35b4d569f22c6c3e77
Reviewed-on: https://chromium-review.googlesource.com/981176Reviewed-by: Lei Zhang <thestig@chromium.org>
Reviewed-by: Steven Holte <holte@chromium.org>
Commit-Queue: Wei Li <weili@chromium.org>
Cr-Commit-Position: refs/heads/master@{#546111}

chrome/browser/printing/print_browsertest.cc

@@ -21,6 +21,7 @@
 #include "chrome/test/base/in_process_browser_test.h"
 #include "chrome/test/base/ui_test_utils.h"
 #include "components/prefs/pref_service.h"
+#include "components/printing/browser/features.h"
 #include "components/printing/browser/print_composite_client.h"
 #include "components/printing/browser/print_manager_utils.h"
 #include "components/printing/common/print_messages.h"
@@ -532,7 +533,9 @@ IN_PROC_BROWSER_TEST_F(PrintBrowserTest, RegularPrinting) {
   ui_test_utils::NavigateToURL(browser(), url);
 
   if (base::CommandLine::ForCurrentProcess()->HasSwitch(
-          switches::kSitePerProcess)) {
+          switches::kSitePerProcess) ||
+      base::FeatureList::IsEnabled(
+          printing::features::kUsePdfCompositorServiceForPrint)) {
     EXPECT_TRUE(IsOopifEnabled());
   } else {
     EXPECT_FALSE(IsOopifEnabled());

testing/variations/fieldtrial_testing_config.json

@@ -3945,6 +3945,24 @@
             ]
         }
     ],
+    "UsePdfCompositorServiceForPrint": [
+        {
+            "platforms": [
+                "chromeos",
+                "linux",
+                "mac",
+                "win"
+            ],
+            "experiments": [
+                {
+                    "name": "UsePdfCompositorServiceForPrint",
+                    "enable_features": [
+                        "UsePdfCompositorServiceForPrint"
+                    ]
+                }
+            ]
+        }
+    ],
     "UserActivityEventLogging": [
         {
             "platforms": [