[SB Delayed Warnings] Add a console message when a download is blocked

SafeBrowsing Delayed Warnings experiment can block a download if the
current page has a delayed warning. In that case, this CL prints a
message to the console.

Bug: 1081317
Change-Id: Ib11dd687ef66eba1dc42e02f1929067f714bb4cc
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2215450Reviewed-by: Daniel Rubery <drubery@chromium.org>
Commit-Queue: Mustafa Emre Acer <meacer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#772499}

chrome/browser/safe_browsing/delayed_warning_navigation_throttle.cc

@@ -10,6 +10,12 @@
 #include "components/safe_browsing/core/features.h"
 #include "content/public/browser/navigation_handle.h"
 
+namespace {
+const char kConsoleMessage[] =
+    "A SafeBrowsing warning is pending on this page, so an attempted download "
+    "was cancelled. See https://crbug.com/1081317 for details.";
+}
+
 namespace safe_browsing {
 
 DelayedWarningNavigationThrottle::DelayedWarningNavigationThrottle(
@@ -44,6 +50,8 @@ DelayedWarningNavigationThrottle::WillProcessResponse() {
   if (navigation_handle()->IsDownload() && observer) {
     // If the SafeBrowsing interstitial is delayed on the page, ignore
     // downloads. The observer will record the histogram entry for this.
+    navigation_handle()->GetWebContents()->GetMainFrame()->AddMessageToConsole(
+        blink::mojom::ConsoleMessageLevel::kWarning, kConsoleMessage);
     return content::NavigationThrottle::CANCEL_AND_IGNORE;
   }
   return content::NavigationThrottle::PROCEED;

chrome/browser/safe_browsing/safe_browsing_blocking_page_test.cc

@@ -1904,9 +1904,16 @@ class SafeBrowsingBlockingPageDelayedWarningBrowserTest
     content::WebContents* contents =
         browser->tab_strip_model()->GetActiveWebContents();
     content::TestNavigationObserver observer(contents);
+    content::WebContentsConsoleObserver console_observer(contents);
+    console_observer.SetPattern(
+        "A SafeBrowsing warning is pending on this page*");
+
     ui_test_utils::NavigateToURL(
         browser, GURL("data:application/octet-stream;base64,SGVsbG8="));
     observer.WaitForNavigationFinished();
+    console_observer.Wait();
+
+    ASSERT_EQ(1u, console_observer.messages().size());
   }
 
   void NavigateAndAssertNoInterstitial() {