port 35c28ce0 (r29758).

original commit message:

    Prior to this patch, we enter a global debug mode whenever a break point
    is set. By entering this mode, all code is deoptimized and activated
    frames are recompiled and redirected to newly compiled debug code.

    After this patch, we only deoptimize/redirect for functions we want to
    debug. Trigger for this is Debug::EnsureDebugInfo, and having DebugInfo
    object attached to the SFI prevents optimization/inlining.

    The result is that we can have optimized code for functions without break
    points alongside functions that do have break points, which are not
    optimized.

BUG=

Review URL: https://codereview.chromium.org/1249503002

Cr-Commit-Position: refs/heads/master@{#29765}