[Top Sites] Validating URLs for "redirects"

Redirects field in TopSitesDatabase is encoded as a space-seprated list
of URLs. But data URLS like "data:text/plain,this text  has space" adds
extra space, so that when decoded, non-URLs like "text" and "has" would
trigger DCHECK in URL() downstream, and crash debug Chrome.

This CL validates redirects URLs when they are read. It is not foolproof
(e.g., "data:text/plan,hidden http://extra.url"), but now we can ponder
how to best fix the root cause, without keeping the crashing bug around.

BUG=358034

Review URL: https://codereview.chromium.org/562993002

Cr-Commit-Position: refs/heads/master@{#296232}

chrome/browser/history/top_sites_database.cc

@@ -90,8 +90,11 @@ std::string GetRedirects(const history::MostVisitedURL& url) {
 void SetRedirects(const std::string& redirects, history::MostVisitedURL* url) {
   std::vector<std::string> redirects_vector;
   base::SplitStringAlongWhitespace(redirects, &redirects_vector);
-  for (size_t i = 0; i < redirects_vector.size(); ++i)
-    url->redirects.push_back(GURL(redirects_vector[i]));
+  for (size_t i = 0; i < redirects_vector.size(); ++i) {
+    GURL redirects_url(redirects_vector[i]);
+    if (redirects_url.is_valid())
+      url->redirects.push_back(redirects_url);
+  }
 }
 
 // Track various failure (and success) cases in recovery code.