Debugger: prepare code for debugging on a per-function basis.

Debugger: prepare code for debugging on a per-function basis.

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.

R=mstarzinger@chromium.org, ulan@chromium.org
BUG=v8:4132
LOG=Y

Review URL: https://codereview.chromium.org/1233073005

Cr-Commit-Position: refs/heads/master@{#29758}