Getting element hiding selectors takes too long

[asmirnov]

Background

We need FilterEngine instance for AdblockWebView to perform resource loading filtering and element hiding.
Currently FilterEngine instance getElementHidingSelectors(String domain) invocation takes about 2 seconds (tested with Samsung Note 3) and it looks not good as the user can't see the page that time.

What to change

One need to understand the reason and optimize it (if possible).

One possible optimization is to request selectors list right after loading starts and at the time we need selectors list it could be ready.

[asmirnov]

C++ code:

__android_log_print(ANDROID_LOG_VERBOSE, APPNAME, "Getting elemhide selectors");
std::vector<std::string> selectors = engine->GetElementHidingSelectors(domain);
__android_log_print(ANDROID_LOG_VERBOSE, APPNAME, "Got them");

log:

09-15 12:19:49.241    8022-8094/org.adblockplus.libadblockplus.webviewapp V/JNI﹕ Getting elemhide selectors
09-15 12:19:51.471    8022-8094/org.adblockplus.libadblockplus.webviewapp V/JNI﹕ Got them

[fhd]

Wladimir pointed out that this might be addressed by #235 (which landed in adblockpluscore revision 6deffadd2643). So updating the core dependency in libadblockplus might already improve things here.

[trev]

This isn't "might" but rather very definitive - performance of ElemHide.getSelectorsByDomain() was very bad before #235, the performance here wasn't optimized at all due to Firefox not using this code path.