Added DCHECK for monotonicTimeToDOMHighResTimeStamp in PerformanceBase

third_party/WebKit/Source/core/paint/FirstMeaningfulPaintDetectorTest.cpp

Index: third_party/WebKit/Source/core/paint/FirstMeaningfulPaintDetectorTest.cpp
diff --git a/third_party/WebKit/Source/core/paint/FirstMeaningfulPaintDetectorTest.cpp b/third_party/WebKit/Source/core/paint/FirstMeaningfulPaintDetectorTest.cpp
index b28b460f85ef86d715936af54fdb218d3b279eff..cc5a52c3dd5de71e30ffdb378921548bc1802583 100644
--- a/third_party/WebKit/Source/core/paint/FirstMeaningfulPaintDetectorTest.cpp
+++ b/third_party/WebKit/Source/core/paint/FirstMeaningfulPaintDetectorTest.cpp
@@ -6,6 +6,8 @@
 
 #include "core/paint/PaintTiming.h"
 #include "core/testing/DummyPageHolder.h"
+#include "core/timing/DOMWindowPerformance.h"
+#include "core/timing/Performance.h"
 #include "testing/gtest/include/gtest/gtest.h"
 
 namespace blink {
@@ -14,7 +16,7 @@ class FirstMeaningfulPaintDetectorTest : public testing::Test {
  protected:
   void SetUp() override {
     m_dummyPageHolder = DummyPageHolder::create(IntSize(800, 600));
-    s_timeElapsed = 0.0;
+    s_timeElapsed = timeOrigin();
     m_originalTimeFunction = setTimeFunctionsForTesting(returnMockTime);
   }
 
@@ -24,6 +26,7 @@ class FirstMeaningfulPaintDetectorTest : public testing::Test {
 
   Document& document() { return m_dummyPageHolder->document(); }
   PaintTiming& paintTiming() { return PaintTiming::from(document()); }
+
   FirstMeaningfulPaintDetector& detector() {
     return paintTiming().firstMeaningfulPaintDetector();
   }
@@ -45,6 +48,14 @@ class FirstMeaningfulPaintDetectorTest : public testing::Test {
     return s_timeElapsed;
   }
 
+  double timeOrigin() {
+    Performance* performance = DOMWindowPerformance::performance(
+        *m_dummyPageHolder->frame().domWindow());
+    if (!performance)
+      return 0.0;
+    return performance->timeOrigin();
+  }
+
   std::unique_ptr<DummyPageHolder> m_dummyPageHolder;
   TimeFunction m_originalTimeFunction;
   static double s_timeElapsed;