Add additional checks to SavePage tests for MHTML

Ensure that all frames in the page loaded from mhtml
have unique origins and content-id urls (except for
the main frame which has a file url).

Bug: none
Change-Id: I0c1d40b82404de2e95e6a7e10dd354826a799d84
Reviewed-on: https://chromium-review.googlesource.com/c/1279188
Commit-Queue: Dmitry Gozman <dgozman@chromium.org>
Reviewed-by: Łukasz Anforowicz <lukasza@chromium.org>
Reviewed-by: Min Qin <qinmin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#599708}

chrome/browser/download/save_page_browsertest.cc

@@ -1072,6 +1072,15 @@ class SavePageOriginalVsSavedComparisonTest
         expected_number_of_frames_in_original_page;
     AssertExpectationsAboutCurrentTab(expected_number_of_frames_in_saved_page,
                                       expected_substrings);
+
+    if (GetParam() == content::SAVE_PAGE_TYPE_AS_MHTML) {
+      std::set<url::Origin> origins;
+      GetCurrentTab(browser())->ForEachFrame(
+          base::BindRepeating(&CheckFrameForMHTML, base::Unretained(&origins)));
+      int unique_origins = origins.size();
+      EXPECT_EQ(expected_number_of_frames_in_saved_page, unique_origins)
+          << "All origins should be unique";
+    }
   }
 
   // Helper method to deduplicate some code across 2 tests.
@@ -1148,6 +1157,18 @@ class SavePageOriginalVsSavedComparisonTest
   static void IncrementInteger(int* i, content::RenderFrameHost* /* unused */) {
     (*i)++;
   }
+
+  static void CheckFrameForMHTML(std::set<url::Origin>* origins,
+                                 content::RenderFrameHost* host) {
+    // See RFC n°2557, section-8.3: "Use of the Content-ID header and CID URLs".
+    const char kContentIdScheme[] = "cid";
+    origins->insert(host->GetLastCommittedOrigin());
+    EXPECT_TRUE(host->GetLastCommittedOrigin().opaque());
+    if (!host->GetParent())
+      EXPECT_TRUE(host->GetLastCommittedURL().SchemeIsFile());
+    else
+      EXPECT_TRUE(host->GetLastCommittedURL().SchemeIs(kContentIdScheme));
+  }
 };
 
 // Test coverage for: