[MIX-DL] Trigger warn/block/silent blocking via feature parameters.

This CL adds feature parameters that create allowlists or blocklists for
warnings, blocking and silent blocking. Finally, it updates the
triggering logic to use those parameters.

The triggering code contains default file extensions which are used when the
feature parameter is not set. These are only used when the user
explicitly enables the feature for testing.

To make testing easier, we:
 - SILENT_BLOCK on files ending in the contrived
   ".silently_block_for_testing".
 - BLOCK files that are executables or archive types, or any download
   that's explicitly user-requested (e.g. from a context menu).
 - WARN on everything else except ".dont_warn_for_testing" files.

Bug: 960819
Change-Id: I006d4e0c3f45b64e3cd84b0ef21cc506988bf5cb
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1984703
Commit-Queue: Joe DeBlasio <jdeblasio@chromium.org>
Reviewed-by: Min Qin <qinmin@chromium.org>
Reviewed-by: Mustafa Emre Acer <meacer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#737470}

chrome/browser/download/chrome_download_manager_delegate.cc

@@ -783,7 +783,7 @@ void ChromeDownloadManagerDelegate::GetMixedContentStatus(
     const base::FilePath& virtual_path,
     const GetMixedContentStatusCallback& callback) {
   DCHECK(download);
-  callback.Run(GetMixedContentStatusForDownload(virtual_path, *download));
+  callback.Run(GetMixedContentStatusForDownload(virtual_path, download));
 }
 
 void ChromeDownloadManagerDelegate::NotifyExtensions(

chrome/browser/download/mixed_content_download_blocking.h

@@ -78,7 +78,8 @@ enum class InsecureDownloadExtensions {
   kEPUB = 19,
   kICS = 20,
   kSVG = 21,
-  kMaxValue = kSVG,
+  kTest = 22,  // Test extensions, e.g. .silently_blocked.
+  kMaxValue = kTest,
 };
 
 struct ExtensionMapping {
@@ -99,6 +100,7 @@ static const ExtensionMapping kExtensionsToEnum[] = {
     {"webp", InsecureDownloadExtensions::kImage},
 
     {"gz", InsecureDownloadExtensions::kArchive},
+    {"gzip", InsecureDownloadExtensions::kArchive},
     {"zip", InsecureDownloadExtensions::kArchive},
     {"bz2", InsecureDownloadExtensions::kArchive},
     {"7z", InsecureDownloadExtensions::kArchive},
@@ -184,6 +186,10 @@ static const ExtensionMapping kExtensionsToEnum[] = {
     {"epub", InsecureDownloadExtensions::kEPUB},
     {"ics", InsecureDownloadExtensions::kICS},
     {"svg", InsecureDownloadExtensions::kSVG},
+
+    {"silently_blocked_for_testing", InsecureDownloadExtensions::kTest},
+    {"warn_for_testing", InsecureDownloadExtensions::kTest},
+    {"dont_warn_for_testing", InsecureDownloadExtensions::kTest},
 };
 
 // Convenience function to assemble a histogram name for download blocking.
@@ -202,6 +208,6 @@ inline std::string GetDLBlockingHistogramName(const std::string& initiator,
 // |item| saved to |path|.  Controlled by kTreatUnsafeDownloadsAsActive.
 download::DownloadItem::MixedContentStatus GetMixedContentStatusForDownload(
     const base::FilePath& path,
-    const download::DownloadItem& item);
+    const download::DownloadItem* item);
 
 #endif  // CHROME_BROWSER_DOWNLOAD_MIXED_CONTENT_DOWNLOAD_BLOCKING_H_

chrome/common/chrome_features.cc

@@ -725,7 +725,6 @@ const base::Feature kAppManagement{"AppManagement",
 // from a secure page
 const base::Feature kTreatUnsafeDownloadsAsActive{
     "TreatUnsafeDownloadsAsActive", base::FEATURE_DISABLED_BY_DEFAULT};
-const char kTreatUnsafeDownloadsAsActiveParamName[] = "ExtensionList";
 
 // Enables or disables the intervention that unloads ad iframes with intensive
 // resource usage.

chrome/common/chrome_features.h

@@ -456,8 +456,6 @@ extern const base::Feature kTLS13HardeningForLocalAnchors;
 
 COMPONENT_EXPORT(CHROME_FEATURES)
 extern const base::Feature kTreatUnsafeDownloadsAsActive;
-COMPONENT_EXPORT(CHROME_FEATURES)
-extern const char kTreatUnsafeDownloadsAsActiveParamName[];
 
 COMPONENT_EXPORT(CHROME_FEATURES)
 extern const base::Feature kHeavyAdIntervention;

tools/metrics/histograms/enums.xml

@@ -33839,6 +33839,7 @@ Called by update_gpu_driver_bug_workaround_entries.py.-->
   <int value="19" label="kEPUB"/>
   <int value="20" label="kICS"/>
   <int value="21" label="kSVG"/>
+  <int value="22" label="kTest"/>
 </enum>
 
 <enum name="InsecureDownloadSecurityStatus">