Run V8 in predictable mode for pdfium_test

samples/pdfium_test.cc

Index: samples/pdfium_test.cc
diff --git a/samples/pdfium_test.cc b/samples/pdfium_test.cc
index a91e13250662f710146f8c639efc4276d1a302b3..d5bf3c0f16993189dba1487fae1c99d43026eb34 100644
--- a/samples/pdfium_test.cc
+++ b/samples/pdfium_test.cc
@@ -582,6 +582,9 @@ int main(int argc, const char* argv[]) {
   v8::Platform* platform = v8::platform::CreateDefaultPlatform();
   v8::V8::InitializePlatform(platform);
   v8::V8::Initialize();
+  // By enabling predicatble mode, V8 won't post any background tasks.
+  const char predictable_flag[] = "--predictable";
+  v8::V8::SetFlagsFromString(predictable_flag, strlen(predictable_flag));
 
 #ifdef V8_USE_EXTERNAL_STARTUP_DATA
   v8::StartupData natives;