Update systrace and profile_chrome's default agent behavior

systrace/profile_chrome/chrome_tracing_agent.py

Index: systrace/profile_chrome/chrome_tracing_agent.py
diff --git a/systrace/profile_chrome/chrome_tracing_agent.py b/systrace/profile_chrome/chrome_tracing_agent.py
index 656a559dcc4670e86f4d6eb398dc18dc1aaa836d..1e8895bd2354fb714515181495fff0c86aeb7d1e 100644
--- a/systrace/profile_chrome/chrome_tracing_agent.py
+++ b/systrace/profile_chrome/chrome_tracing_agent.py
@@ -14,7 +14,7 @@ from systrace import trace_result
 from systrace import tracing_agents
 
 
-_DEFAULT_CHROME_CATEGORIES = '_DEFAULT_CHROME_CATEGORIES'
+DEFAULT_CHROME_CATEGORIES = '_DEFAULT_CHROME_CATEGORIES'

[Chris Craik, 2016/10/06 19:56:37]

why is this just a string that refers to its previous variable name? shouldn't
this be a list of categories?

[Zhen Wang, 2016/10/06 19:58:37]

This is a magic string used by Chrome for Android.

See
https://cs.chromium.org/chromium/src/content/public/android/java/src/org/chro...

 _HEAP_PROFILE_MMAP_PROPERTY = 'heapprof.mmap'
 
 
@@ -163,8 +163,7 @@ def add_options(parser):
                          'Chrome\'s default categories. Chrome tracing can be '
                          'disabled with "--categories=\'\'". Use "list" to '
                          'see the available categories.',
-                         metavar='CHROME_CATEGORIES', dest='chrome_categories',
-                         default=_DEFAULT_CHROME_CATEGORIES)
+                         metavar='CHROME_CATEGORIES', dest='chrome_categories')
   chrome_opts.add_option('--trace-cc',
                          help='Deprecated, use --trace-frame-viewer.',
                          action='store_true')