[ Profiler ] Fix CPU sample streaming sending only a single sample block instead of a chain of blocks
[ Profiler ] Fix CPU sample streaming sending only a single sample block instead of a chain of blocks

A pointer to a single SampleBlockBuffer was being passed in while
building a profile instead of a reference to SampleBlockListProcessor.
This also could lead to a segfault if there were no blocks to process.

TEST=CQ + manual testing in Flutter engine

Change-Id: I1e2903cf718da7b32747553c2ed1efcb78b62c86
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/214441
Commit-Queue: Ben Konyi <67ffcaedcc3dc3d87dddb9627b72dd41756b31b1@google.com>
Reviewed-by: Siva Annamalai <2e618a8cbd7bb6b3d4409061ae407d692a098546@google.com>

dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk