Revert of Enable isolate on Linux release builder.

scripts/slave/recipe_modules/chromium_tests/api.py

Index: scripts/slave/recipe_modules/chromium_tests/api.py
diff --git a/scripts/slave/recipe_modules/chromium_tests/api.py b/scripts/slave/recipe_modules/chromium_tests/api.py
index 458434f86aa7e25ac69caa6fb2948959e8aecbf9..4c95fc617c9f40069e06c48bb6c75054aeca9858 100644
--- a/scripts/slave/recipe_modules/chromium_tests/api.py
+++ b/scripts/slave/recipe_modules/chromium_tests/api.py
@@ -237,7 +237,10 @@
         self.m.chromium_android.findbugs()
 
       has_swarming_tests = any(t.uses_swarming for t in tests)
-      if has_swarming_tests:
+      if bot_config.get('use_isolate'):
+        self.m.isolate.find_isolated_tests(self.m.chromium.output_dir)
+      # TODO(phajdan.jr): Always use the below codepath once fully tested.
+      elif has_swarming_tests:
         isolated_targets = [t.name for t in tests if t.uses_swarming]
         self.m.isolate.find_isolated_tests(
             self.m.chromium.output_dir, targets=list(set(isolated_targets)))