Output stacktraces on WebGL conformance failure.

content/test/gpu/gpu_tests/webgl_conformance.py

Index: content/test/gpu/gpu_tests/webgl_conformance.py
diff --git a/content/test/gpu/gpu_tests/webgl_conformance.py b/content/test/gpu/gpu_tests/webgl_conformance.py
index 803b44ece243650210f800d54ddaf217c918d1b5..be917d7771dd4de0f997d376ee6a05f21b46458c 100644
--- a/content/test/gpu/gpu_tests/webgl_conformance.py
+++ b/content/test/gpu/gpu_tests/webgl_conformance.py
@@ -84,7 +84,11 @@ class WebglConformanceValidator(gpu_test_base.ValidatorBase):
 
   def ValidateAndMeasurePage(self, page, tab, results):
     if not _DidWebGLTestSucceed(tab):
-      raise page_test.Failure(_WebGLTestMessages(tab))
+      is_valid_dump, trace_output = tab.browser.GetStackTrace()

[Ken Russell (switch to Gerrit), 2016/06/16 17:48:01]

I was concerned about the performance cost of doing this after every page run
but realize that this will only be executed after a failure, which should not be
the common case.

+      messages = _WebGLTestMessages(tab)
+      if is_valid_dump:
+        messages += '\nStack Trace:\n' + trace_output
+      raise page_test.Failure(messages)
 
   def CustomizeBrowserOptions(self, options):
     # --test-type=gpu is used only to suppress the "Google API Keys are missing"