chromedriver: fix an bugprone-string-integer-assignment instance

`string::operator=(int)` turns into `string::operator=(char)` by casting
the RHS of the assignment, so this code turns into `env = "\x01"`; `env
= "1"` was probably what was intended.

Bug: 1130867
Change-Id: I8a1a1e268c65246c35d864314502fb4aab62e6b4
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2425333Reviewed-by: John Chen <johnchen@chromium.org>
Commit-Queue: George Burgess <gbiv@chromium.org>
Cr-Commit-Position: refs/heads/master@{#811841}

chrome/test/chromedriver/chrome_launcher.cc

@@ -473,11 +473,11 @@ Status LaunchDesktopChrome(network::mojom::URLLoaderFactory* factory,
 
 #if defined(OS_WIN)
     // EnvironmentMap uses wide string
-    options.environment[L"CHROME_HEADLESS"] = 1;
+    options.environment[L"CHROME_HEADLESS"] = L"1";
     options.environment[L"BREAKPAD_DUMP_LOCATION"] =
         base::SysUTF8ToWide(capabilities.minidump_path);
 #else
-    options.environment["CHROME_HEADLESS"] = 1;
+    options.environment["CHROME_HEADLESS"] = "1";
     options.environment["BREAKPAD_DUMP_LOCATION"] = capabilities.minidump_path;
 #endif