Adding a ToPrettyString method to ConvertableToTracedValue.

Adding a ToPrettyString method to ConvertableToTracedValue.

Also adds a nice ToPrettyString method to TraceEventArgument which produces
a much more human readable output. See the change in
scheduler_state_machine_unittest which uses this feature.

The output (trimmed) goes from;
===============================================================
[ RUN      ] SchedulerStateMachineTest.TestAnimateAfterCommitBeforeDraw
../../cc/scheduler/scheduler_state_machine_unittest.cc:1792: Failure
Value of: SchedulerStateMachine::ActionToString(state.NextAction())
  Actual: "ACTION_DRAW_AND_SWAP_IF_POSSIBLE"
Expected: SchedulerStateMachine::ActionToString(SchedulerStateMachine::ACTION_ANIMATE)
Which is: "ACTION_ANIMATE"
{"major_state":{"begin_impl_frame_state":"BEGIN_IMPL_FRAME_STATE_INSIDE_DEA
DLINE","commit_state":"COMMIT_STATE_WAITING_FOR_ACTIVATION","forced_redraw_
ending_swaps_":0,"pending_tree_is_ready_for_activation":false,"skip_begin_m
ain_frame_to_reduce_latency":false,"skip_next_begin_main_frame_to_reduce_la
tency":false,"swap_used_incomplete_tile":false,"visible":true}}
[  FAILED  ] SchedulerStateMachineTest.TestAnimateAfterCommitBeforeDraw (1
ms)
===============================================================

To the much easier to read output (trimmed) below;
===============================================================
[ RUN      ] SchedulerStateMachineTest.TestAnimateAfterCommitBeforeDraw
../../cc/scheduler/scheduler_state_machine_unittest.cc:1792: Failure
Value of: SchedulerStateMachine::ActionToString(state.NextAction())
  Actual: "ACTION_DRAW_AND_SWAP_IF_POSSIBLE"
Expected: SchedulerStateMachine::ActionToString(SchedulerStateMachine::ACTION_ANIMATE)
Which is: "ACTION_ANIMATE"
{
   "major_state": {
      "begin_impl_frame_state": "BEGIN_IMPL_FRAME_STATE_INSIDE_DEADLINE",
      "output_surface_state_": "OUTPUT_SURFACE_ACTIVE"
   },
   "major_timestamps_in_ms": {
      "0_interval": 16.666,
      "6_deadline": 208595868.986
   },
   "minor_state": {
      "active_tree_needs_first_draw": false,
      "visible": true
   }
}
[  FAILED  ] SchedulerStateMachineTest.TestAnimateAfterCommitBeforeDraw (1 ms)
===============================================================

[mithro-old, 2014-10-01 15:16:46]

mithro@mithis.com changed reviewers:
+ nduca@chromium.org, yurys@chromium.org

[mithro-old, 2014-10-01 15:16:47]

Hi Nat / Yury,

This is a very small addition to the tracing to support converting a TracedValue
into a more human readable "pretty" output. 

I've found this functionality very useful in a number of cc unit tests which
have good AsValue support.

I would like to see --trace-to-console using this ToPrettyString but haven't had
a chance to look at how much work that would be. Specially since --trace-to-file
has now been added which is better for getting the "raw" output anyway.

I initially was using a command line flag to control if ToString was
pretty/non-pretty printed but found that it has too much of a board impact.

What do you think?

Tim 'mithro' Ansell

[dsinclair, 2014-10-01 17:39:45]

On 2014/10/01 15:16:47, mithro wrote:
> Hi Nat / Yury,
> 
> This is a very small addition to the tracing to support converting a
TracedValue
> into a more human readable "pretty" output. 
> 
> I've found this functionality very useful in a number of cc unit tests which
> have good AsValue support.
> 
> I would like to see --trace-to-console using this ToPrettyString but haven't
had
> a chance to look at how much work that would be. Specially since
--trace-to-file
> has now been added which is better for getting the "raw" output anyway.
> 
> I initially was using a command line flag to control if ToString was
> pretty/non-pretty printed but found that it has too much of a board impact.
> 
> What do you think?
> 
> Tim 'mithro' Ansell


Personally, I'm not a huge fan of this. I don't think we want to be encouraging
people to be using the Convertables in unit tests, as you don't necessarily know
when they've changed.

Now that we have the trace to file, it feels like it would be better to use that
when debugging and open the trace in trace-viewer.

[yurys, 2014-10-02 12:07:05]

The idea of having TracedValue was to eventually change the implementation so
that it writes directly into its buffer without creating intermediate Value
objects. Having ToPrettyString would hamper this as we would need to keep
structure of the value in order to prettify it in some rare cases.

[JimSelf27, 2014-10-11 10:51:47]

jimself27@gmail.com changed reviewers:
+ JimSelf27@gmail.com