Build webkit_unit_tests in chromium.webrtc.

Recently a WebRTC CL had to be reverted because it was breaking Blink
compilation. Since WebRTC integrates with it, it makes sense to build
these tests in order to discover compiler errors before submitting
WebRTC CLs.

Bug: None
Change-Id: I01d88695e641c37c58e4bb000e22844fa0862fe9
Reviewed-on: https://chromium-review.googlesource.com/c/1277991Reviewed-by: Patrik Höglund <phoglund@chromium.org>
Reviewed-by: John Budorick <jbudorick@chromium.org>
Commit-Queue: Mirko Bonadei <mbonadei@chromium.org>
Cr-Commit-Position: refs/heads/master@{#600086}

testing/buildbot/tryserver.webrtc.json

@@ -8,7 +8,8 @@
       "content_browsertests",
       "content_unittests",
       "jingle_unittests",
-      "remoting_unittests"
+      "remoting_unittests",
+      "webkit_unit_tests"
     ]
   },
   "linux_chromium_compile": {
@@ -19,7 +20,8 @@
       "content_unittests",
       "jingle_unittests",
       "remoting_unittests",
-      "remoting/webapp:webapp"
+      "remoting/webapp:webapp",
+      "webkit_unit_tests"
     ]
   },
   "mac_chromium_compile": {
@@ -30,7 +32,8 @@
       "content_unittests",
       "jingle_unittests",
       "remoting_unittests",
-      "remoting/webapp:webapp"
+      "remoting/webapp:webapp",
+      "webkit_unit_tests"
     ]
   },
   "win_chromium_compile": {
@@ -41,7 +44,8 @@
       "content_unittests",
       "jingle_unittests",
       "remoting_unittests",
-      "remoting/webapp:webapp"
+      "remoting/webapp:webapp",
+      "webkit_unit_tests"
     ]
   }
 }

testing/buildbot/waterfalls.pyl

@@ -3919,6 +3919,7 @@
           'content_unittests',
           'jingle_unittests',
           'remoting_unittests',
+          'webkit_unit_tests',
         ],
       },
       'linux_chromium_compile': {
@@ -3930,6 +3931,7 @@
           'jingle_unittests',
           'remoting_unittests',
           'remoting/webapp:webapp',
+          'webkit_unit_tests',
         ],
       },
       'mac_chromium_compile': {
@@ -3941,6 +3943,7 @@
           'jingle_unittests',
           'remoting_unittests',
           'remoting/webapp:webapp',
+          'webkit_unit_tests',
         ],
       },
       'win_chromium_compile': {
@@ -3952,6 +3955,7 @@
           'jingle_unittests',
           'remoting_unittests',
           'remoting/webapp:webapp',
+          'webkit_unit_tests',
         ],
       },
     },