Fix regression while I worked on removing support for isolate_dependency_tracked.

It's a trivial change. The next swarming_client/ DEPS roll will enforce that no
further regression occurs.

TBR=vadimsh@chromium.org
NOTRY=true
BUG=

Review URL: https://codereview.chromium.org/636283010

Cr-Commit-Position: refs/heads/master@{#300669}

content/content_unittests.isolate

@@ -60,7 +60,7 @@
     }],
     ['OS=="linux" and libpeer_target_type=="loadable_module"', {
       'variables': {
-        'isolate_dependency_tracked': [
+        'files': [
           '<(PRODUCT_DIR)/lib/libpeerconnection.so',
         ],
       },
@@ -106,7 +106,7 @@
     }],
     ['OS=="win" and libpeer_target_type=="loadable_module"', {
       'variables': {
-        'isolate_dependency_tracked': [
+        'files': [
           '<(PRODUCT_DIR)/libpeerconnection.dll',
         ],
       },