Stop emitting warnings for mime types not recognized by Android.

net/android/network_library.cc

Index: net/android/network_library.cc
diff --git a/net/android/network_library.cc b/net/android/network_library.cc
index 6a5b592f5e5db81cb1d7c6ffafe3f8146e7b02f4..b53cefe4783cab5bb6f431a5e157414cdec24504 100644
--- a/net/android/network_library.cc
+++ b/net/android/network_library.cc
@@ -81,11 +81,8 @@ bool GetMimeTypeFromExtension(const std::string& extension,
       Java_AndroidNetworkLibrary_getMimeTypeFromExtension(
           env, extension_string.obj());
 
-  if (!ret.obj()) {
-    LOG(WARNING) << "Call to getMimeTypeFromExtension failed for extension: "
-        << extension;
+  if (!ret.obj())
     return false;
-  }
   *result = ConvertJavaStringToUTF8(ret);
   return true;
 }