Proper error handling was missing, using VERIFY to crash in debug builds, while release builds would ignore the error and leak the attribute memory. The check of attribute type consistency was changed to a RTC_DCHECK. Also removes a large number of uses of the deprecated VERIFY macro. BUG=webrtc:6424 Review-Url: https://codereview.webrtc.org/2665343002 Cr-Commit-Position: refs/heads/master@{#16413}