[WEEX-465][Android]fix performance point interactionTime record bug

[lucky-chen]

• use jsCreateFinish flag to replace mEnd
• call onElementChanged() just in add/rm element action
• proteted mWXSDKInstance.getWXPerformance() null ptr

[weex-bot]

	Warnings
⚠️	No Changelog changes!
⚠️	Potential BREAK CHANGE. Modify public in android/sdk/src/main/java/com/taobao/weex/ui/module/WXTimerModule.java without metion it in commit message. You'd better add '@notdanger' in your commit log.
⚠️	Potential BREAK CHANGE. Modify public in android/sdk/src/main/java/com/taobao/weex/WXSDKInstance.java without metion it in commit message. You'd better add '@notdanger' in your commit log.

	Messages
📖	danger test finished.

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