Shard browser_tests 5x for PlzNavigate.

testing/buildbot/chromium.fyi.json

 {
   "Android Asan Builder Tests (dbg)": {
     "gtest_tests": [
       {
         "args": [
           "--tool=asan"
         ],
         "swarming": {
           "can_use_on_swarming_builders": false
         },
@@ skipping 853 matching lines @@
   "Android VR Tests": {},
   "Browser Side Navigation Linux": {
     "gtest_tests": [
       {
         "args": [
           "--enable-browser-side-navigation",
           "--test-launcher-filter-file=../../testing/buildbot/filters/browser-side-navigation.linux.browser_tests.filter",
           "--test-launcher-retry-limit=6"
         ],
         "swarming": {
-          "can_use_on_swarming_builders": true
+          "can_use_on_swarming_builders": true,
+          "shards": 5
         },
         "test": "browser_tests"
       },
       {
         "args": [
           "--enable-browser-side-navigation",
           "--test-launcher-filter-file=../../testing/buildbot/filters/browser-side-navigation.linux.content_browsertests.filter"
         ],
         "swarming": {
           "can_use_on_swarming_builders": true
@@ skipping 11140 matching lines @@
       },
       {
         "swarming": {
           "can_use_on_swarming_builders": true
         },
         "test": "views_unittests"
       }
     ]
   }
 }