Check for empty MHTML archive resource

The passed SharedBuffer data may be null if the MHTML archive is
empty. Added a check for this.

Bug: 831443
Change-Id: Id675c801c7df94c9596d4a91a9ba5c7458f9936b
Reviewed-on: https://chromium-review.googlesource.com/1063033
Commit-Queue: Jian Li <jianli@chromium.org>
Reviewed-by: Kent Tamura <tkent@chromium.org>
Cr-Commit-Position: refs/heads/master@{#560741}

third_party/blink/renderer/core/frame/mhtml_archive_test.cc

@@ -372,6 +372,15 @@ TEST_F(MHTMLArchiveTest, MHTMLDate) {
   EXPECT_EQ(mhtml_date(), archive->Date());
 }
 
+TEST_F(MHTMLArchiveTest, EmptyArchive) {
+  char* buf = nullptr;
+  scoped_refptr<SharedBuffer> data =
+      SharedBuffer::Create(buf, static_cast<size_t>(0u));
+  KURL http_url = ToKURL("http://www.example.com");
+  MHTMLArchive* archive = MHTMLArchive::Create(http_url, data.get());
+  EXPECT_EQ(nullptr, archive);
+}
+
 }  // namespace test
 
 }  // namespace blink

third_party/blink/renderer/platform/mhtml/mhtml_archive.cc

@@ -149,6 +149,10 @@ MHTMLArchive::MHTMLArchive() = default;
 
 MHTMLArchive* MHTMLArchive::Create(const KURL& url,
                                    scoped_refptr<const SharedBuffer> data) {
+  // |data| may be null if archive file is empty.
+  if (!data)
+    return nullptr;
+
   // MHTML pages can only be loaded from local URLs, http/https URLs, and
   // content URLs(Android specific).  The latter is now allowed due to full
   // sandboxing enforcement on MHTML pages.