Switch profiler from isolates to threads [second landing]

Switch profiler from isolates to threads

- API breakage: Dart_IsolateBlocked, Dart_IsolateUnblocked -> Dart_ThreadDisableProfiling, Dart_ThreadEnableProfiling.
- Remove IsolateProfilerData.
- Move thread at blocking call count from isolate to thread.
- Always interrupt threads unless they are blocked.
- We can no longer count "idle" ticks.
- Only record sample if thread is the current mutator of an isolate.
- Refactor ThreadInterrupterCallback to ensure that Thread* is valid.

Threads are only ever sent signals if ThreadInterruptsEnabled is true. Which is controlled by two functions:

void DisableThreadInterrupts();
void EnableThreadInterrupts();

R=asiva@google.com, iposva@google.com

Committed: https://github.com/dart-lang/sdk/commit/ceb12c4f69ff02ba5ffa9f7dc047399cb69e4930

[Cutch, 2015-11-04 15:27:53]

Description was changed from

==========
Switch profiler from isolates to threads

- API breakage: Dart_IsolateBlocked, Dart_IsolateUnblocked ->
Dart_ThreadDisableProfiling, Dart_ThreadEnableProfiling.
- Remove IsolateProfilerData.
- Move thread at blocking call count from isolate to thread.
- Always interrupt threads unless they are blocked.
- We can no longer count "idle" ticks.
- Only record sample if thread is the current mutator of an isolate.
- Refactor ThreadInterrupterCallback to ensure that Thread* is valid.

Threads are only ever sent signals if ThreadInterruptsEnabled is true. Which is
controlled by two functions:

void DisableThreadInterrupts();
void EnableThreadInterrupts();

R=asiva@google.com, iposva@google.com
==========

to

==========
Switch profiler from isolates to threads

- API breakage: Dart_IsolateBlocked, Dart_IsolateUnblocked ->
Dart_ThreadDisableProfiling, Dart_ThreadEnableProfiling.
- Remove IsolateProfilerData.
- Move thread at blocking call count from isolate to thread.
- Always interrupt threads unless they are blocked.
- We can no longer count "idle" ticks.
- Only record sample if thread is the current mutator of an isolate.
- Refactor ThreadInterrupterCallback to ensure that Thread* is valid.

Threads are only ever sent signals if ThreadInterruptsEnabled is true. Which is
controlled by two functions:

void DisableThreadInterrupts();
void EnableThreadInterrupts();

R=asiva@google.com, iposva@google.com
==========

[Cutch, 2015-11-04 15:28:32]

This is the exact same CL as https://codereview.chromium.org/1412733008/ and I
am relanding it now that I've (hopefully) worked around the run_vm_tests Windows
only hang.

[Cutch, 2015-11-04 15:59:22]

Committed patchset #1 (id:1) manually as
ceb12c4f69ff02ba5ffa9f7dc047399cb69e4930 (presubmit successful).