Remove browser-unpin-trace key.

As far as I can tell, it hasn't been used usefully in investigations
in years, and StackTrace members can cause problems on Android
(https://crbug.com/1056216 -- admittedly due to bugs elsewhere,
so removing this is papering over symptoms in a way. But if this
is unused, we should remove it for that reason anyways).

Bug: 1056216
Change-Id: I32e4f468a9f8dd5cb6ff4ffb2938f25c86af7530
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2163261Reviewed-by: Robert Sesek <rsesek@chromium.org>
Commit-Queue: Nico Weber <thakis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#762154}

chrome/browser/browser_process_impl.cc

@@ -1376,18 +1376,7 @@ void BrowserProcessImpl::ApplyDefaultBrowserPolicy() {
 
 void BrowserProcessImpl::Pin() {
   DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
-
-  // CHECK(!IsShuttingDown());
-  if (IsShuttingDown()) {
-    // TODO(rsesek): Consider removing this trace, but it has been helpful
-    // in debugging several shutdown crashes (https://crbug.com/113031,
-    // https://crbug.com/625646, and https://crbug.com/779829).
-    static crash_reporter::CrashKeyString<1024> browser_unpin_trace(
-        "browser-unpin-trace");
-    crash_reporter::SetCrashKeyStringToStackTrace(
-        &browser_unpin_trace, release_last_reference_callstack_);
-    CHECK(false);
-  }
+  CHECK(!IsShuttingDown());
 }
 
 void BrowserProcessImpl::Unpin() {
@@ -1401,7 +1390,6 @@ void BrowserProcessImpl::Unpin() {
   if (!quit_closure_)
     return;
 #endif
-  release_last_reference_callstack_ = base::debug::StackTrace();
 
   DCHECK(!shutting_down_);
   shutting_down_ = true;

chrome/browser/browser_process_impl.h

@@ -15,7 +15,6 @@
 #include <memory>
 #include <string>
 
-#include "base/debug/stack_trace.h"
 #include "base/macros.h"
 #include "base/memory/ref_counted.h"
 #include "base/sequence_checker.h"
@@ -381,10 +380,6 @@ class BrowserProcessImpl : public BrowserProcess,
 
   std::unique_ptr<BrowserProcessPlatformPart> platform_part_;
 
-  // TODO(eroman): Remove this when done debugging 113031. This tracks
-  // the callstack which released the final module reference count.
-  base::debug::StackTrace release_last_reference_callstack_;
-
   // Lazily initialized.
   std::unique_ptr<WebRtcLogUploader> webrtc_log_uploader_;