Make all the readonly attributes in Device Capabilities valid.

[kygx-legend]

Bug=XWALK-2162

[crosswalk-trybot]

Testing patch series with kygx-legend/crosswalk@8aeaf52 as its head.

Bot	Status
Crosswalk Linux	[FAILED 💔](https://build.crosswalk-project.org/try/builders/Crosswalk Linux/builds/1786)
Crosswalk Android-X86	[SUCCESS 💚](https://build.crosswalk-project.org/try/builders/Crosswalk Android-X86/builds/1786)
Crosswalk Tizen 3 Common	[SUCCESS 💚](https://build.crosswalk-project.org/try/builders/Crosswalk Tizen 3 Common/builds/1375)
Crosswalk Tizen 3 Mobile	[SUCCESS 💚](https://build.crosswalk-project.org/try/builders/Crosswalk Tizen 3 Mobile/builds/1791)
Crosswalk Tizen IVI	[SUCCESS 💚](https://build.crosswalk-project.org/try/builders/Crosswalk Tizen IVI/builds/1777)

[kygx-legend]

This PR is the same as #2316 . @halton , plz help review.

[halton]

lgtm, will merge after trybot get green.

[kygx-legend]

It's strange to fail. Seems failed at xwalk_sysapps_browsertest. I will find out the cause.

[halton]

Yes, the previous try 1785 is green. So should be regression for this commit, please fix.

[crosswalk-trybot]

Testing patch series with kygx-legend/crosswalk@be2e17a as its head.

Bot	Status
Crosswalk Linux	[FAILED 💔](https://build.crosswalk-project.org/try/builders/Crosswalk Linux/builds/1827)
Crosswalk Tizen IVI	[SUCCESS 💚](https://build.crosswalk-project.org/try/builders/Crosswalk Tizen IVI/builds/1819)
Crosswalk Tizen 3 Common	[SUCCESS 💚](https://build.crosswalk-project.org/try/builders/Crosswalk Tizen 3 Common/builds/1417)
Crosswalk Android-X86	[SUCCESS 💚](https://build.crosswalk-project.org/try/builders/Crosswalk Android-X86/builds/1827)

[kygx-legend]

@halton , I found it failed at this line createConstClone(data) for listener. It should be wrong. I try hard to understand the EventTargetPrototype's structure but can not understand totally. I can not find where the real recieved data is. Try to add createConstClone in line 190, 230 or 245 and all are failed. Could you please have a look at this?

[qjia7]

@legendlee1314 Do you still work on this? I think this point doesn't need to change. Just keep the old design.

[liyingzh]

@halton I tested adding the changed code on crosswalk@35b73bc7d43d8dcab600c2afedcdcf21de0651ee, building with ninja -C out/Release successful, may trybot test again.

[halton]

@liyingzh yes, please force update the repo, trybot will restart.

[crosswalk-trybot]

Testing patch series with kygx-legend/crosswalk@a1d7f4a as its head.

Bot	Status
Crosswalk Linux	[FAILED 💔](https://build.crosswalk-project.org/try/builders/Crosswalk Linux/builds/2674)
Crosswalk Tizen 3 Common	[SUCCESS 💚](https://build.crosswalk-project.org/try/builders/Crosswalk Tizen 3 Common/builds/2263)
Crosswalk Android-X86	[SUCCESS 💚](https://build.crosswalk-project.org/try/builders/Crosswalk Android-X86/builds/2674)
Crosswalk Tizen IVI	[SUCCESS 💚](https://build.crosswalk-project.org/try/builders/Crosswalk Tizen IVI/builds/2667)

[kygx-legend]

@liyingzh , it is still failed at xwalk_sysapps_browsertest from log. Could you please reproduce the test?