error_page_populator: minor optimization

This code should do nothing if error_html is null. This moves
the check earlier.

BUG=none
TEST=none

Change-Id: I568c5ece3c2e1aca23e91480918ce1a35a07fa55
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2324654
Commit-Queue: Scott Violet <sky@chromium.org>
Commit-Queue: Bo <boliu@chromium.org>
Auto-Submit: Scott Violet <sky@chromium.org>
Reviewed-by: Bo <boliu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#792463}

components/android_system_error_page/error_page_populator.cc

@@ -26,15 +26,15 @@ constexpr char kThrottledErrorDescription[] =
 
 void PopulateErrorPageHtml(const blink::WebURLError& error,
                            std::string* error_html) {
+  if (!error_html)
+    return;
+
   std::string err;
   if (error.reason() == net::ERR_TEMPORARILY_THROTTLED)
     err = kThrottledErrorDescription;
   else
     err = net::ErrorToString(error.reason());
 
-  if (!error_html)
-    return;
-
   // Create the error page based on the error reason.
   GURL gurl(error.url());
   std::string url_string = gurl.possibly_invalid_spec();

components/android_system_error_page/error_page_populator.h

@@ -14,7 +14,7 @@ struct WebURLError;
 namespace android_system_error_page {
 
 // Populates |error_html| to display an error page with an Android system feel
-// for |error|.
+// for |error|. Does nothing if |error_html| is null.
 void PopulateErrorPageHtml(const blink::WebURLError& error,
                            std::string* error_html);