Log stack trace when ObjectWatcher::StartWatching() is called.

base/win/object_watcher.cc

Index: base/win/object_watcher.cc
diff --git a/base/win/object_watcher.cc b/base/win/object_watcher.cc
index ebe596f3a6ec0686ed8cce3e2ae60a00f826b8d5..0b9d7a0f5ac94d47319f2751aeadb196476e9b97 100644
--- a/base/win/object_watcher.cc
+++ b/base/win/object_watcher.cc
@@ -5,6 +5,7 @@
 #include "base/win/object_watcher.h"
 
 #include "base/bind.h"
+#include "base/debug/alias.h"
 #include "base/logging.h"
 
 namespace base {
@@ -40,6 +41,7 @@ bool ObjectWatcher::StartWatching(HANDLE object, Delegate* delegate) {
                          delegate);
   object_ = object;
   origin_loop_ = MessageLoop::current();
+  stack_trace_ = base::debug::StackTrace();
 
   if (!RegisterWaitForSingleObject(&wait_object_, object, DoneWaiting,
                                    this, INFINITE, wait_flags)) {
@@ -97,6 +99,10 @@ void ObjectWatcher::Signal(Delegate* delegate) {
   // StartWatching(). As a result, we save any state we need and clear previous
   // watcher state before signaling the delegate.
   HANDLE object = object_;
+  // Alias the stack trace where the watch was started so it'll be available in
+  // minidumps.
+  base::debug::StackTrace stack_trace = stack_trace_;
+  base::debug::Alias(&stack_trace);
   StopWatching();
   delegate->OnObjectSignaled(object);
 }