Fix debugging of async code

Fix debugging of async code

Make sure the debugger finds the closure function containing the body
of async functions, but not the synthetic function that generates the
future.

Change the way the debugger sets one-time breakpoints. Instead of
compiling the function and instrumenting all safe-points, set a
breakpoint marked as “one-shot” at the beginning of the function
and wait until the function is compiled. Then, once it fires, it
gets automatically deleted.

Finally, be smarter how we resolve breakpoints in compiled code.
The compiler rearranges code in await expressions, which tripped
up the debugger. This change makes sure we select the lowest compiled
code address only within the line containing the requested breakpoint
position.

R=iposva@google.com

Committed: https://code.google.com/p/dart/source/detail?r=42368

[hausner, 2014-12-13 00:59:27]

hausner@google.com changed reviewers:
+ iposva@google.com

[Ivan Posva, 2014-12-15 16:36:54]

LGTM

-Ivan

https://codereview.chromium.org/805573003/diff/1/runtime/vm/debugger.cc
File runtime/vm/debugger.cc (right):

https://codereview.chromium.org/805573003/diff/1/runtime/vm/debugger.cc#newco...
runtime/vm/debugger.cc:1417: // First pass: find the lowest token position
within the given range.
What you are looking for here is the lowest breakpointable token position,
correct? It was not necessarily clear from the comment.

[hausner, 2014-12-15 18:20:25]

Committed patchset #2 (id:20001) manually as r42368 (presubmit successful).

[hausner, 2014-12-15 18:21:46]

https://codereview.chromium.org/805573003/diff/1/runtime/vm/debugger.cc
File runtime/vm/debugger.cc (right):

https://codereview.chromium.org/805573003/diff/1/runtime/vm/debugger.cc#newco...
runtime/vm/debugger.cc:1417: // First pass: find the lowest token position
within the given range.
On 2014/12/15 16:36:54, Ivan Posva wrote:
> What you are looking for here is the lowest breakpointable token position,
> correct? It was not necessarily clear from the comment.

Yes. I clarified the comments.