Exporter/Trace: Refactor to use TimeLimitedHandler.

[songy23]

Updates #1880.

The goal of this change is to reduce the code duplication added in recent exporter PRs (e.g #1884 #1885 #1886), as a follow up of #1887.

[dmichel1]

hey @songy23 i'm curious about the deadlines you are adding to all the trace exporters. Is this to avoid blocking the SpanExporterImplThread since some of the exporters are running in that thread?

Can the Stackdriver exporter still block the SpanExporterImplThread even though the work is being delegated to the grpc thread pool?

[rghetia]

LGTM

[songy23]

Is this to avoid blocking the SpanExporterImplThread since some of the exporters are running in that thread?

Correct, see #1767 (comment).

Can the Stackdriver exporter still block the SpanExporterImplThread even though the work is being delegated to the grpc thread pool?

Stackdriver exporter still blocks the SpanExporterImplThread before deadline is exceeded. After that the exporter just drops any undelivered spans. This is the first step described in #1767 (comment). The second step is to make exporters async (non-blocking).

[dmichel1]

@songy23 makes sense thanks! Glad i'm following along.