Errors on API 27

[paulo-raca]

As we talked on #74, the unit test fail on API 27.

I've confirmed it on x86 and x86_64 emulators, but I didn't test on any arm/arm64 device.

[rk700]

I compare the code of both 8.0 and 8.1:

http://androidxref.com/8.0.0_r4/xref/art/runtime/mirror/dex_cache.cc#210
http://androidxref.com/8.1.0_r33/xref/art/runtime/mirror/dex_cache.cc#216

It seems that the cached method array is no longer initialized with the helper trampoline.

Moreover, the cached method array is of type MethodDexCacheType instead of ArtMethod in 8.1, which I didn't realize before.

http://androidxref.com/8.1.0_r33/xref/art/runtime/art_method.h#743
http://androidxref.com/8.0.0_r4/xref/art/runtime/art_method.h#704

I believe that the change in array type leads to the crash.

[rk700]

Here's a workaround which might work:

    if(backupMethod) {// do method backup
        if(SDKVersion < ANDROID_O2) {

I've tried on x86 emulator and it works. But not yet for x86_64 and ARM devices which I don't have either.

[paulo-raca]

Thanks!

[rk700]

This commit 632342d resolves the issue finally.