Run V8 in predictable mode for pdfium_test

testing/embedder_test.cpp

Index: testing/embedder_test.cpp
diff --git a/testing/embedder_test.cpp b/testing/embedder_test.cpp
index 9b21609978c58656abf248a509070f1352d118c7..70c32af8c758c5b07c1ee406f2184d85bcbc1d29 100644
--- a/testing/embedder_test.cpp
+++ b/testing/embedder_test.cpp
@@ -193,6 +193,9 @@ EmbedderTest::~EmbedderTest() {
 
 void EmbedderTest::SetUp() {
     v8::V8::InitializeICU();
+    // 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
     ASSERT_TRUE(GetExternalData(g_exe_path_, "natives_blob.bin", &natives_));