Fix one implicit 64-bit -> 32-bit implicit conversion in a PPAPI test.

../../ppapi/tests/test_url_loader.cc:877:11: warning: implicit conversion loses integer precision: 'int64_t' (aka 'long long') to 'int32_t' (aka 'int') [-Wshorten-64-to-32]
          total_bytes_to_be_received);
          ^~~~~~~~~~~~~~~~~~~~~~~~~~

BUG=879657

Change-Id: I152f456368131fe7a2891ff0c97bf83f26ef0906
Reviewed-on: https://chromium-review.googlesource.com/c/1220173
Commit-Queue: Raymes Khoury <raymes@chromium.org>
Reviewed-by: Raymes Khoury <raymes@chromium.org>
Cr-Commit-Position: refs/heads/master@{#600182}

ppapi/tests/test_url_loader.cc

@@ -874,7 +874,7 @@ std::string TestURLLoader::TestUntendedLoad() {
     loader.GetDownloadProgress(&bytes_received, &total_bytes_to_be_received);
     if (total_bytes_to_be_received <= 0)
       return ReportError("URLLoader::GetDownloadProgress total size",
-          total_bytes_to_be_received);
+                         static_cast<int32_t>(total_bytes_to_be_received));
     if (bytes_received == total_bytes_to_be_received)
       break;
     // Yield if we're on the main thread, so that URLLoader can receive more