Reland "AppCache: Add padding to cross-origin responses."

This is a reland of 85b389caa7d725cdd31f59e9a2b79ff54804b7b7

Initialized CacheRecord::padding_size to 0.

Original change's description:
> AppCache: Add padding to cross-origin responses.
>
> Bug: 918293
> Change-Id: I4f16640f06feac009d6bbbb624951da6d2669f6c
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1488059
> Commit-Queue: Staphany Park <staphany@chromium.org>
> Reviewed-by: Victor Costan <pwnall@chromium.org>
> Reviewed-by: Marijn Kruisselbrink <mek@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#644624}

Bug: 918293
Change-Id: Ie1d3f99c7e8a854d33255a4d66243da2ce16441c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1539906
Reviewed-by: Victor Costan <pwnall@chromium.org>
Commit-Queue: Staphany Park <staphany@chromium.org>
Cr-Commit-Position: refs/heads/master@{#644719}
  void Verify_ExclusionNotFound(GURL expected_url, int phase) {
    EXPECT_EQ(expected_url, delegate()->found_url_);
    EXPECT_TRUE(delegate()->found_manifest_url_.is_empty());
    EXPECT_EQ(blink::mojom::kAppCacheNoCacheId, delegate()->found_cache_id_);
    EXPECT_EQ(0, delegate()->found_group_id_);
    EXPECT_EQ(blink::mojom::kAppCacheNoResponseId,
              delegate()->found_entry_.response_id());
    EXPECT_EQ(blink::mojom::kAppCacheNoResponseId,
              delegate()->found_fallback_entry_.response_id());
    EXPECT_TRUE(delegate()->found_namespace_entry_url_.is_empty());
    EXPECT_EQ(0, delegate()->found_entry_.types());
    EXPECT_EQ(0, delegate()->found_fallback_entry_.types());

    if (phase == 1) {
      PushNextTask(
          base::BindOnce(&AppCacheStorageImplTest::Verify_ExclusionNotFound,
                         base::Unretained(this), kOnlineNamespace, 2));
      storage()->FindResponseForMainRequest(kOnlineNamespace, GURL(),
                                            delegate());
      return;
    }
    if (phase == 2) {
      PushNextTask(base::BindOnce(
          &AppCacheStorageImplTest::Verify_ExclusionNotFound,
          base::Unretained(this), kOnlineNamespaceWithinFallback, 3));
      storage()->FindResponseForMainRequest(kOnlineNamespaceWithinFallback,
                                            GURL(), delegate());
      return;
    }

    TestFinished();
  }

  void Verify_ExclusionNotFound(GURL expected_url, int phase) {
    EXPECT_EQ(expected_url, delegate()->found_url_);
    EXPECT_TRUE(delegate()->found_manifest_url_.is_empty());
    EXPECT_EQ(blink::mojom::kAppCacheNoCacheId, delegate()->found_cache_id_);
    EXPECT_EQ(0, delegate()->found_group_id_);
    EXPECT_EQ(blink::mojom::kAppCacheNoResponseId,
              delegate()->found_entry_.response_id());
    EXPECT_EQ(blink::mojom::kAppCacheNoResponseId,
              delegate()->found_fallback_entry_.response_id());
    EXPECT_TRUE(delegate()->found_namespace_entry_url_.is_empty());
    EXPECT_EQ(0, delegate()->found_entry_.types());
    EXPECT_EQ(0, delegate()->found_fallback_entry_.types());

    if (phase == 1) {
      PushNextTask(
          base::BindOnce(&AppCacheStorageImplTest::Verify_ExclusionNotFound,
                         base::Unretained(this), kOnlineNamespace, 2));
      storage()->FindResponseForMainRequest(kOnlineNamespace, GURL(),
                                            delegate());
      return;
    }
    if (phase == 2) {
      PushNextTask(base::BindOnce(
          &AppCacheStorageImplTest::Verify_ExclusionNotFound,
          base::Unretained(this), kOnlineNamespaceWithinFallback, 3));
      storage()->FindResponseForMainRequest(kOnlineNamespaceWithinFallback,
                                            GURL(), delegate());
      return;
    }

    TestFinished();
  }
