Re-land: Fix flatbuffers failures-mode

This re-lands this CL:
https://chromium-review.googlesource.com/c/chromium/src/+/1503614

Which was reverted here:
https://chromium-review.googlesource.com/c/chromium/src/+/1504597

There's one additional change, which is to ensure that windows
runtime_libs are available as data_deps. This omission was causing
failures on win_chromium_dbg_ng.

Bug: 938020
Change-Id: Id0196d86097f938d046c7936e619d1c7cf8174c3
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1506124Reviewed-by: Dirk Pranke <dpranke@chromium.org>
Commit-Queue: Charlie Harrison <csharrison@chromium.org>
Cr-Commit-Position: refs/heads/master@{#638684}

testing/scripts/run_flatbuffers_unittests.py

@@ -40,15 +40,16 @@ def main():
     exe = os.path.join('.', 'flatbuffers_unittests')
 
   env = os.environ.copy()
+  failures = []
   with common.temporary_file() as tempfile_path:
     rc = xvfb.run_executable([exe], env, stdoutfile=tempfile_path)
 
     # The flatbuffer tests do not really conform to anything parsable, except
     # that they will succeed with "ALL TESTS PASSED".
     with open(tempfile_path) as f:
-      failures = f.read()
-      if failures == "ALL TESTS PASSED\n":
-        failures = []
+      output = f.read()
+      if output != "ALL TESTS PASSED\n":
+        failures = [output]
 
   with open(args.isolated_script_test_output, 'w') as fp:
     json.dump({'valid': True,'failures': failures}, fp)

third_party/flatbuffers/BUILD.gn

@@ -17,6 +17,10 @@ source_set("flatbuffers") {
     "src/include/flatbuffers/stl_emulation.h",
   ]
 
+  if (is_win) {
+    data_deps = [ "//build/win:runtime_libs" ]
+  }
+
   configs -= [ "//build/config/compiler:chromium_code" ]
   configs += [ "//build/config/compiler:no_chromium_code" ]