Use absolute paths in Android section in tools/BUILD.gn.

In the logic to run tests on Android, the path is currently relative.
This only works when V8 is standalone. When V8 is checkout in another
project, the path is wrong. The build_with_chromium check only helps
with Chromium, but there are other V8 embedders.

Change-Id: I52640a664deb39e5959ed3cc9dc79fd7b6d68758
Reviewed-on: https://chromium-review.googlesource.com/1189096Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Commit-Queue: Lei Zhang <thestig@chromium.org>
Cr-Commit-Position: refs/heads/master@{#55439}

tools/BUILD.gn

@@ -30,11 +30,11 @@ group("v8_android_test_runner_deps") {
 
   if (is_android && !build_with_chromium) {
     data_deps = [
-      "../build/android:test_runner_py",
+      "//build/android:test_runner_py",
     ]
     data = [
       # This is used by android.py, but not included by test_runner_py above.
-      "../third_party/catapult/devil/devil/android/perf/",
+      "//third_party/catapult/devil/devil/android/perf/",
     ]
   }
 }