[webapi][xwalk-2561] Update codes based on Chromium implement

- mp4a.40.8/mp4v.20.8 is also not supported in chromium 38, need use mp4a.40.2/mp4a.40 instead.
- Verified on Crosswalk 9.38.204.0

Impacted tests(approved): new 0, update 2, delete 0
Unit test platform: [Tizen IVI][Android]
Unit test result summary: pass 2, fail 0, block 0
[wrt][XWALK-1668]Add new audiopolicy testcase

Impacted TCs num(approved): New audiopolicy 7, update multiuser 3, deleted 0
Implacted TCs num(designed): New 2, Update 0, deleted 0
Unit test platform: [tizen]
UT result: Pass:7, Fail 1, block 1
Fail: Crosswalk_AudioPolicy_WebappAudioPlay: two webapp audio can be play at the same time
Block:Crosswalk_AudioPolicy_Muliple_Sinks: No bluetooth headset
[doc] Transfer pdf to md in doc directory
[webapi]Change ref test in webapi-style-css3-tests

Impacted tests(approved):new 0,update 5,delete 0
Unit test platform:[Android]
Unit test result summary:pass 5,fail 0,block 0
[webapi]Change ref test in tct-fonts-css3-tests

Impacted tests(approved):new 0,update 48,delete 0
Unit test platform:[Android]
Unit test result summary:pass 44,fail 4,block 0
[webapi]Change ref test in tct-canvas-html5-tests

Impacted tests(approved):new 0,update 5,delete 0
Unit test platform:[Android]
Unit test result summary:pass 0,fail 5,block 0
[webapi]Change ref test in tct-color-css3-tests

Impacted tests(approved):new 0,update 19,delete 0
Unit test platform:[Android]
Unit test result summary:pass 11,fail 8,block 0
Merge pull request #934 from kangxu/kangxu/wrt/doc/addMD

[doc] Transfer pdf to md in doc directory
Merge pull request #933 from haoxli/haoxli/webapi/xwalk-2561-video

[webapi][xwalk-2561] Update codes based on Chromium implement
Merge pull request #931 from linshen/shenlin/addaudioplicy

[wrt][XWALK-1668]Add new audiopolicy testcase
[wrt] Add subcase and type to tests.xml
[usecase-webapi] Demo for adding pluggable step info

Impacted TCs num(approve): New 0, Update 0, Delete 1
Unit test Platform: Andriod
Unit test result summary: Pass 0, Fail 0, Blocked 0
Merge pull request #896 from JianfengXu/xujf/usecase/step

[usecase-webapi] Demo for adding pluggable step info
Merge pull request #938 from wanghongjuan/wanghongjuan/wrt/subcase

[wrt] Add subcase and type to tests.xml
[misc-webapi] Fix the spelling errors for uiautomation

- Fail Reason: child-src, base-uri and plugin-types are not supported.

Impacted TCs num(approved): New 0, Update 25, Delete 0
Unit test Platform: [Tizen IVI]
Unit test result summary: Pass 21, Fail 4, Blocked 0
[cordova][xwalk-2427] Add debug step for eclipse case

Impacted tests(approved): new 0, update 1, delete 0
Unit test platform: [Nexus 5]
Unit test result summary: pass 1, fail 0, block 0
[webapi]update ref case from manual type to auto

Impacted tests(approved):new 0,update 57,delete 0
Unit test platform:[Android]
Unit test result summary:pass 10,fail 47,block 0
[webapi][XWALK-1914] update 21 case status for SIMD

- Fail Reason: Some methods in SIMD is not supported.

Impacted TCs num(apporved): New 0, Update 21, Delete 0
Unit test Platform: Andriod
Unit test result summary: Pass 21, Fail 0, Blocked 0
[wrt-usecase][xwalk-2394] Update TCs due to feature resolved

Impacted TCs num(approved): New 2, Update 4, Delete 0
Unit test Platform: Android
Android test result summary: Pass 6, Fail 0, Block 0
Merge pull request #943 from wanghongjuan/wanghongjuan/usecase/xwalk-2394

[wrt-usecase][xwalk-2394] Update TCs due to feature resolved