Correctly report callstack when current function is FunctionCall builtin

When current function is FunctionCall builtin we have no reliable way to determine its caller function (in many cases the top of the sampled stack contains address of the caller but sometimes it does not). Instead of dropping the sample or its two top frames we simply mark the caller frame as '(unresolved function)'. It seems like a better approach that dropping whole sample as knowing the top function and the rest of the stack the user should be able to figure out what the caller was.

This change adds builtin id to CodeEntry objects. It will be used later to add similar top frame analysis for FunctionApply and probably other builtins.

BUG=None
R=jkummerow@chromium.org, loislo@chromium.org

Review URL: https://codereview.chromium.org/18316004

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@15426 ce2b1a6d-e550-0410-aec6-3dcde31c8c00