Misc debugger enhancements and bug fixes.

Misc debugger enhancements and bug fixes.

1. Added gdb style debugger commands (and their shortcuts) for d8.
These include:
- s[tep] : step into the current statement.
- s[tep]i[n]: step into the current statement with the minimum step.
- n[ext] : step to the next statement.
- fin[ish] : step out of the current function.
- cond : setting conditions on breakpoints.
- d[elete] : deletes breakpoints.
- en[able]|dis[able]: enables/disables breakpoints including
exception breakpoints.
- ignore : ignores a breakpoint for a specified period.
- inf[o] ar[gs] : info on arguments of the current function.
- inf[o] lo[cals] : info on local vars of the current function.
- inf[o] br[eakpoints] : info on breakpoints.
- l[ist] : similar to source, but allows the user to continually
dump subsequent lines of source code either in the
forward or backward direction.
- quit / exit / disconnect : terminates the remote debugger
session.

NOTE: Active breakpoints will automatically be disabled when
the remote debugger detaches. This allows v8 to continue to
run without worrying about a loss of a debugger session.

2. Added support for breaking the debugger by simply typing ENTER.
The break command is now optional.

3. Once the debugger is broken, the user can now just type ENTER
to repeat the last command. This is useful to functionality that
needs to be invoked repeatedly e.g. step, list.

4. Added more verbose descriptions in d8's help.

5. Fixed a line and column number offset bug in the listing of breakpoint
line and column numbers.

6. Added a gc command to allow GCs to be requested from the debugger
interface. The plumbing for requesting different types of GCs is
there, but the underlying implementation currently only triggers a
full mark-compact GC. The command also returns the before and after
sizes of the heap.

7. Added trace json, and flags commands that are not published in help.
trace json is used for tracing the debugger packets send from and
received by d8. flags is for setting v8 flags. These are useful for
people debugging v8 itself, but not necessarily users of v8.

8. Added the ability to enable and disable break on all / uncaught
exceptions in to d8.

9. Added a fix to prevent the Debugger Agent from being re-instantiated
if one already exists.

10. Added the ability to filter results of the script command by matching
text or numbers on the results.

11. Added v8 flags to enable/disable the sending of debugger BeforeCompile,
AfterCompile, and ScriptCollected events.

12. Fixed some undefined value bugs that resulted in v8 or the debugger
failing.

13. Added a few minor WEBOS__ customizations (analogous to ANDROID
customizations).

Patch by Mark Lam from Hewlett-Packard Development Company, LP

Review URL: http://codereview.chromium.org/5980006

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@6180 ce2b1a6d-e550-0410-aec6-3dcde31c8c00