Store the NSEvent.description in a crash key in -[BrowserCrApplication sendEvent:].

chrome/browser/chrome_browser_application_mac.mm

Index: chrome/browser/chrome_browser_application_mac.mm
diff --git a/chrome/browser/chrome_browser_application_mac.mm b/chrome/browser/chrome_browser_application_mac.mm
index 5b4967e7564bc58e91cae4cec7a0ab3fda63c0c2..5a63b9f03ebecf9a81ed2bf24256cdf933e70347 100644
--- a/chrome/browser/chrome_browser_application_mac.mm
+++ b/chrome/browser/chrome_browser_application_mac.mm
@@ -351,6 +351,9 @@ void CancelTerminate() {
 }
 
 - (void)sendEvent:(NSEvent*)event {
+  base::debug::ScopedCrashKey crash_key(
+      crash_keys::mac::kNSEvent, base::SysNSStringToUTF8([event description]));
+
   base::mac::CallWithEHFrame(^{
     switch (event.type) {
       case NSLeftMouseDown: