Web Inspector: [CPU Profile] Taking profile crashes renderer.

Web Inspector: [CPU Profile] Taking profile crashes renderer.
https://bugs.webkit.org/show_bug.cgi?id=108072

Patch by Eugene Klyuchnikov <eustas@chromium.org> on 2013-01-29
Reviewed by Yury Semikhatsky.

Source/WebCore:

Test: inspector/profiler/cpu-profiler-agent-crash-on-start.html

Fixed null-pointer access.

* bindings/v8/ScriptProfiler.cpp:
(WebCore::ScriptProfiler::start): Fixed null-pointer access.
(WebCore::ScriptProfiler::stop): Ditto.

LayoutTests:

Added test to check that ProfilerAgent start/stop doesn't crash.

* inspector/profiler/cpu-profiler-agent-crash-on-start-expected.txt: Added.
* inspector/profiler/cpu-profiler-agent-crash-on-start.html: Added.

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@141094 268f45cc-cd09-0410-ab3c-d52691b4dbfc