Build browser tests on all gpu release bots

testing/buildbot/chromium.gpu.json

 {
   "AAAAA1 AUTOGENERATED FILE DO NOT EDIT": {},
   "AAAAA2 See generate_buildbot_json.py to make changes": {},
-  "GPU Linux Builder": {},
+  "GPU Linux Builder": {
+    "additional_compile_targets": [
+      "browser_tests"
+    ]
+  },
   "GPU Linux Builder (dbg)": {},
-  "GPU Mac Builder": {},
+  "GPU Mac Builder": {
+    "additional_compile_targets": [
+      "browser_tests"
+    ]
+  },
   "GPU Mac Builder (dbg)": {},
-  "GPU Win Builder": {},
+  "GPU Win Builder": {
+    "additional_compile_targets": [
+      "browser_tests"
+    ]
+  },
   "GPU Win Builder (dbg)": {},
   "Linux Debug (NVIDIA)": {
     "gtest_tests": [
       {
         "args": [
           "--use-gpu-in-tests",
           "--test-launcher-retry-limit=0"
         ],
         "swarming": {
           "can_use_on_swarming_builders": true,
@@ skipping 2651 matching lines @@
             {
               "gpu": "10de:104a",
               "os": "Windows-2008ServerR2-SP1"
             }
           ]
         }
       }
     ]
   }
 }