Add support in devserver to stage debug_breakpad.tar.xz

BUG=chromium:623739
TEST=unittest, local run devserver
curl "http://localhost:8082/stage?artifacts=symbols_only&files=&archive_url= \
  gs_path_to_build"

Change-Id: I7fbff78a91218b408c3f054a5742b6d887734bdb
Reviewed-on: https://chromium-review.googlesource.com/393008
Commit-Ready: Dan Shi <dshi@google.com>
Tested-by: Dan Shi <dshi@google.com>
Reviewed-by: Mike Frysinger <vapier@chromium.org>
diff --git a/artifact_info.py b/artifact_info.py
index a6ff6f7..4c0484a 100644
--- a/artifact_info.py
+++ b/artifact_info.py
@@ -67,6 +67,10 @@
 # Tarball containing debug symbols for the given build.
 SYMBOLS = 'symbols'
 
+# A compressed tarball containing only sym files of debug symbols for the
+# given build.
+SYMBOLS_ONLY = 'symbols_only'
+
 # The factory test image.
 FACTORY_IMAGE = 'factory_image'
 
diff --git a/build_artifact.py b/build_artifact.py
index 22e0560..d5a7039 100755
--- a/build_artifact.py
+++ b/build_artifact.py
@@ -37,6 +37,7 @@
 AUTOTEST_COMPRESSED_FILE = 'autotest.tar.bz2'
 AUTOTEST_SERVER_PACKAGE_FILE = 'autotest_server_package.tar.bz2'
 DEBUG_SYMBOLS_FILE = 'debug.tgz'
+DEBUG_SYMBOLS_ONLY_FILE = 'debug_breakpad.tar.xz'
 FACTORY_FILE = 'ChromeOS-factory*.zip'
 FACTORY_SHIM_FILE = 'factory_image.zip'
 FIRMWARE_FILE = 'firmware_from_source.tar.bz2'
@@ -621,6 +622,9 @@
 _AddCrOSArtifact(artifact_info.FIRMWARE, Artifact, FIRMWARE_FILE)
 _AddCrOSArtifact(artifact_info.SYMBOLS, BundledArtifact, DEBUG_SYMBOLS_FILE,
                  files_to_extract=['debug/breakpad'])
+_AddCrOSArtifact(artifact_info.SYMBOLS_ONLY, BundledArtifact,
+                 DEBUG_SYMBOLS_ONLY_FILE,
+                 files_to_extract=['debug/breakpad'])
 _AddCrOSArtifact(artifact_info.FACTORY_IMAGE, BundledArtifact, FACTORY_FILE,
                  files_to_extract=[devserver_constants.FACTORY_IMAGE_FILE])
 _AddCrOSArtifact(artifact_info.FACTORY_SHIM_IMAGE, BundledArtifact,