Fix a DCHECK in WillHandleBrowserAboutURL()

The code in FixupURL does not properly handle "about:blank" variants
where some letter in "blank" is uppercase. This CL fixes the issue by
returning "about:blank" when the lowercase of the input URL is
"about:blank".

Bug: 857201
Change-Id: Ia1ff719d142ae8f2a346cbca231e52a811e9b77c
Reviewed-on: https://chromium-review.googlesource.com/1117627Reviewed-by: Ehsan Karamad <ekaramad@chromium.org>
Reviewed-by: Peter Kasting <pkasting@chromium.org>
Commit-Queue: Ehsan Karamad <ekaramad@chromium.org>
Cr-Commit-Position: refs/heads/master@{#571147}

components/url_formatter/url_fixer.cc

@@ -551,10 +551,16 @@ GURL FixupURL(const std::string& text, const std::string& desired_tld) {
     return GURL();
   }
 
-  // Parse and rebuild about: and chrome: URLs, except about:blank.
+  // 'about:blank' is special-cased in various places in the code so it
+  // shouldn't be transformed into 'chrome://blank' as the code below will do.
+  // Instead, just make sure it's all lowercase, so direct string comparisons
+  // elsewhere will work.
+  if (base::LowerCaseEqualsASCII(trimmed, url::kAboutBlankURL))
+    return GURL(url::kAboutBlankURL);
+
+  // Parse and rebuild about: and chrome: URLs.
   bool chrome_url =
-      !base::LowerCaseEqualsASCII(trimmed, url::kAboutBlankURL) &&
-      ((scheme == url::kAboutScheme) || (scheme == kChromeUIScheme));
+      (scheme == url::kAboutScheme) || (scheme == kChromeUIScheme);
 
   // For some schemes whose layouts we understand, we rebuild it.
   if (chrome_url ||

components/url_formatter/url_fixer_unittest.cc

@@ -306,6 +306,7 @@ struct FixupCase {
     {"about:foo", "chrome://foo/"},
     {"about:version", "chrome://version/"},
     {"about:blank", "about:blank"},
+    {"About:blaNk", "about:blank"},
     {"about:usr:pwd@hst:20/pth?qry#ref", "chrome://hst/pth?qry#ref"},
     {"about://usr:pwd@hst/pth?qry#ref", "chrome://hst/pth?qry#ref"},
     {"chrome:usr:pwd@hst/pth?qry#ref", "chrome://hst/pth?qry#ref"},