cc: Add missing xdisplaycheck data dependency for tests.

This adds xdisplaycheck as a dependency of cc_unittests_run for gyp isolate
builds. xdisplaycheck is used by the isolate script to run cc_unittests so it
must be built when cc_unittests is built.

BUG=464062

Review URL: https://codereview.chromium.org/981683002

Cr-Commit-Position: refs/heads/master@{#319529}

cc/BUILD.gn

@@ -923,3 +923,5 @@ test("cc_perftests") {
     "//ui/gl",
   ]
 }
+# When adding support for isolates, please have a look at run-time dependencies
+# in the cc_unittests_run target in cc_tests.gyp.

cc/cc_tests.gyp

@@ -460,6 +460,17 @@
           'sources': [
             'cc_unittests.isolate',
           ],
+          'conditions': [
+            # crbug.com/464062 xdisplaycheck is used to run cc_unittests_run on
+            # the linux try bots when using X11.
+            ['OS=="linux" and use_ozone==0',
+              {
+                'dependencies': [
+                  '../tools/xdisplaycheck/xdisplaycheck.gyp:xdisplaycheck',
+                ],
+              }
+            ],
+          ],
         },
       ],
     }],