Add browser_tests, content_browsertests and extensions_browsertests to WebKit Linux Oilpan

testing/buildbot/chromium.webkit.json

 {
   "Linux ChromiumOS Tests (1)": {
     "gtest_tests": [
       {
         "swarming": {
           "can_use_on_swarming_builders": true
         },
         "test": "accessibility_unittests"
       },
       {
@@ skipping 822 matching lines @@
         "test": "blink_heap_unittests"
       },
       {
         "swarming": {
           "can_use_on_swarming_builders": true
         },
         "test": "blink_platform_unittests"
       },
       {
         "swarming": {
+          "can_use_on_swarming_builders": true,
+          "shards": 20
+        },
+        "test": "browser_tests"
+      },
+      {
+        "swarming": {
+          "can_use_on_swarming_builders": true
+        },
+        "test": "content_browsertests"
+      },
+      {
+        "swarming": {
+          "can_use_on_swarming_builders": true
+        },
+        "test": "extensions_browsertests"
+      },
+      {
+        "swarming": {
           "can_use_on_swarming_builders": true
         },
         "test": "webkit_unit_tests"
       },
       {
         "swarming": {
           "can_use_on_swarming_builders": true
         },
         "test": "wtf_unittests"
       }
@@ skipping 743 matching lines @@
         "name": "webkit_lint",
         "script": "webkit_lint.py"
       },
       {
         "name": "webkit_python_tests",
         "script": "webkit_python_tests.py"
       }
     ]
   }
 }