Add Resource memory size test

First, I broke the calculation by change initialization order:
https://chromium-review.googlesource.com/c/chromium/src/+/1948393
That caused apparent memory improvement.
Then another my CL fixed the order:
https://chromium-review.googlesource.com/c/chromium/src/+/2099668
Now bots computes memory size appropriately as same as before.

This CL adds a test so that no such false regression.

Bug: 1062837
Change-Id: If76707cae97f0037664facd901bfea45241c66f6
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2114479Reviewed-by: Yutaka Hirano <yhirano@chromium.org>
Commit-Queue: Yoichi Osato <yoichio@chromium.org>
Cr-Commit-Position: refs/heads/master@{#753462}

third_party/blink/renderer/platform/loader/fetch/resource.h

@@ -419,6 +419,10 @@ class PLATFORM_EXPORT Resource : public GarbageCollected<Resource>,
   // The caller owns the |clock| which must outlive the Resource.
   static void SetClockForTesting(const base::Clock* clock);
 
+  size_t CalculateOverheadSizeForTest() const {
+    return CalculateOverheadSize();
+  }
+
  protected:
   Resource(const ResourceRequestHead&,
            ResourceType,

third_party/blink/renderer/platform/loader/fetch/resource_test.cc

@@ -575,4 +575,11 @@ TEST(ResourceTest, StaleWhileRevalidateCacheControlWithRedirect) {
   EXPECT_TRUE(resource->StaleRevalidationRequested());
 }
 
+// This is a regression test for https://crbug.com/1062837.
+TEST(ResourceTest, DefaultOverheadSize) {
+  const KURL url("http://127.0.0.1:8000/foo.html");
+  auto* resource = MakeGarbageCollected<MockResource>(url);
+  EXPECT_EQ(resource->CalculateOverheadSizeForTest(), resource->OverheadSize());
+}
+
 }  // namespace blink