[ios/web] Don't dcheck when rewriting placeholder URLs.

about:blank?query URLs are expected after fixup.

Change-Id: I155245731e7f3623e7f27ad8ba76ddb4cc55fc53
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1582960
Commit-Queue: Justin Cohen <justincohen@chromium.org>
Reviewed-by: Eugene But <eugenebut@chromium.org>
Auto-Submit: Justin Cohen <justincohen@chromium.org>
Cr-Commit-Position: refs/heads/master@{#658731}

ios/chrome/browser/browser_about_rewriter.cc

@@ -36,7 +36,10 @@ bool WillHandleWebBrowserAboutURL(GURL* url, web::BrowserState* browser_state) {
   *url = url_formatter::FixupURL(url->possibly_invalid_spec(), std::string());
 
   // Check that about: URLs are fixed up to chrome: by url_formatter::FixupURL.
-  DCHECK((*url == url::kAboutBlankURL) || !url->SchemeIs(url::kAboutScheme));
+  // 'about:blank' is special-cased in various places in the code so it
+  // shouldn't be transformed.
+  DCHECK(!url->SchemeIs(url::kAboutScheme) ||
+         (url->path() == url::kAboutBlankPath));
 
   // url_formatter::FixupURL translates about:foo into chrome://foo/.
   if (!url->SchemeIs(kChromeUIScheme))

ios/chrome/browser/browser_about_rewriter_unittest.cc

@@ -20,7 +20,8 @@ TEST_F(BrowserAboutRewriterTest, NtpTest) {
   EXPECT_FALSE(WillHandleWebBrowserAboutURL(&url, nil));
 }
 
-// Test that about|chrome://about is rewritten to chrome-urls.
+// Test that about|chrome://about is rewritten to chrome-urls and about:blank
+// is not.
 TEST_F(BrowserAboutRewriterTest, AboutTest) {
   GURL url = GURL("about:about");
   EXPECT_FALSE(WillHandleWebBrowserAboutURL(&url, /*browser_state=*/nullptr));
@@ -29,6 +30,10 @@ TEST_F(BrowserAboutRewriterTest, AboutTest) {
   url = GURL("chrome://about/");
   EXPECT_FALSE(WillHandleWebBrowserAboutURL(&url, /*browser_state=*/nullptr));
   EXPECT_EQ(url, GURL("chrome://chrome-urls/"));
+
+  url = GURL("about:blank?for=");
+  EXPECT_FALSE(WillHandleWebBrowserAboutURL(&url, /*browser_state=*/nullptr));
+  EXPECT_EQ(url, GURL("about:blank?for="));
 }
 
 // Test that about|chrome://sync is rewritten to sync-internals.