After doing so much investigation i found solution for this issue. clear and type was not working in Android 6.0 if the context is webview.
MobileElement element = (MobileElement) appDriver.findElement(By.xpath(expression));
el.clear();
if(null!=el&&null!=el.getText() && el.getText().length()>0){
el.click();
Runtime.getRuntime().exec(“adb shell input keyevent 123”);
int leng=el.getText().length();
logger.debug(“Lenght of the text is” + leng);
for(int i=0;i<leng;i++){
appDriver.sendKeyEvent(AndroidKeyCode.BACKSPACE);
}
}
el.sendKeys(text);