Re-enable android-binary-size trybot ForTest check only for dex symbols.

Reset limit back to 0 for 'ForTest' check and only check dex symbols
since those are actionable vs native symbols which are much less so.

Bug: 1012373
Change-Id: I725f50068c2f433b30000ed16e999ff7c31e06ce
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1896119Reviewed-by: Andrew Grieve <agrieve@chromium.org>
Commit-Queue: Andrew Grieve <agrieve@chromium.org>
Auto-Submit: Mohamed Heikal <mheikal@chromium.org>
Cr-Commit-Position: refs/heads/master@{#712145}

tools/binary_size/trybot_commit_size_checker.py

@@ -172,8 +172,8 @@ def _CreateUncompressedPakSizeDeltas(symbols):
 
 
 def _CreateTestingSymbolsDeltas(symbols):
-  testing_symbols = symbols.WhereNameMatches('ForTest').WhereDiffStatusIs(
-      models.DIFF_STATUS_ADDED)
+  testing_symbols = symbols.WhereIsDex().WhereNameMatches(
+      'ForTest').WhereDiffStatusIs(models.DIFF_STATUS_ADDED)
   lines = None
   if len(testing_symbols):
     lines = list(describe.GenerateLines(testing_symbols, summarize=False))