[bgmode] Log the unpin stack trace to Crash Keys

chrome/browser/browser_process_impl.cc

Index: chrome/browser/browser_process_impl.cc
diff --git a/chrome/browser/browser_process_impl.cc b/chrome/browser/browser_process_impl.cc
index ace2dd1165390eff49e9720bffa9c943afbf6e5e..d307797a1eec0d06c27d6ce71abfd95c05b3698a 100644
--- a/chrome/browser/browser_process_impl.cc
+++ b/chrome/browser/browser_process_impl.cc
@@ -15,7 +15,7 @@
 #include "base/bind.h"
 #include "base/bind_helpers.h"
 #include "base/command_line.h"
-#include "base/debug/alias.h"
+#include "base/debug/crash_logging.h"
 #include "base/debug/leak_annotations.h"
 #include "base/files/file_path.h"
 #include "base/location.h"
@@ -77,6 +77,7 @@
 #include "chrome/common/chrome_constants.h"
 #include "chrome/common/chrome_paths.h"
 #include "chrome/common/chrome_switches.h"
+#include "chrome/common/crash_keys.h"
 #include "chrome/common/extensions/chrome_extensions_client.h"
 #include "chrome/common/extensions/extension_process_policy.h"
 #include "chrome/common/features.h"
@@ -1314,10 +1315,8 @@ void BrowserProcessImpl::Pin() {
 
   // CHECK(!IsShuttingDown());
   if (IsShuttingDown()) {
-    // Copy the stacktrace which released the final reference onto our stack so
-    // it will be available in the crash report for inspection.
-    base::debug::StackTrace callstack = release_last_reference_callstack_;
-    base::debug::Alias(&callstack);
+    base::debug::SetCrashKeyToStackTrace(crash_keys::kBrowserUnpinTrace,

[eroman, 2016/12/14 20:40:24]

Have you tested that this works?

I am pretty sure crash keys are not dynamic -- you need to register them in
advance (see RegisterChromeCrashKeys()).

[dgn, 2016/12/16 19:10:42]

Thanks! Sadly we don't have a reliable repro for the bug and because of the
CHECK/crash below it's not testable. So I'm not sure how to exercise that path.

+                                         release_last_reference_callstack_);
     CHECK(false);

[eroman, 2016/12/14 20:40:24]

I imagine there should be something like:

// TODO(crbug.com/625646): Temporary instrumentation

[dgn, 2016/12/16 19:10:42]

Not sure if temporary... you added that almost 5 years ago :)
https://codereview.chromium.org/9375037

[eroman, 2016/12/16 19:28:16]

Heh, nothing quite as durable as a "temporary" hack :)

   }
 }