V8DebuggerAgentImpl::m_skipAllPaused is moved to V8Debugger.
V8DebuggerAgentImpl::didPaused doesn't return shouldBreak flag and called only when break is required and stack trace presented.
V8DebuggerAgentImpl doesn't store paused context.
Logic of conversion step-next at return into step-in is moved to debug.cc.

BUG=none
R=dgozman@chromium.org,yangguo@chromium.org

Review-Url: https://codereview.chromium.org/2668763003
Cr-Commit-Position: refs/heads/master@{#42907}