[Extensions] Add coarse metrics for extension function performance

extensions/browser/extension_function.cc

Index: extensions/browser/extension_function.cc
diff --git a/extensions/browser/extension_function.cc b/extensions/browser/extension_function.cc
index 5c6319fabaa6c9eb20b6aa1aaa8fb2385e8167fb..0c2af6b2a7834a40587d10f29612c2fd09096de7 100644
--- a/extensions/browser/extension_function.cc
+++ b/extensions/browser/extension_function.cc
@@ -10,6 +10,7 @@
 #include "base/macros.h"
 #include "base/memory/ptr_util.h"
 #include "base/memory/singleton.h"
+#include "base/metrics/histogram_macros.h"
 #include "base/synchronization/lock.h"
 #include "content/public/browser/notification_source.h"
 #include "content/public/browser/notification_types.h"
@@ -406,6 +407,15 @@ void ExtensionFunction::SendResponseImpl(bool success) {
     results_.reset(new base::ListValue());
 
   response_callback_.Run(type, *results_, GetError(), histogram_value());
+
+  // TODO(devlin): Once we have a baseline metric for how long functions take,

[lazyboy, 2016/05/03 01:00:01]

Addition to the notes, I think referring to the bug (608561) here would be
helpful for the reader to get more context.
(Or if you want to track this second stage bucketing thing in a separate bug)

[Devlin, 2016/05/03 17:03:36]

Done.

+  // we can create a handful of buckets and record the function name so that we
+  // can find what the fastest/slowest are.
+  // Note: Certain functions perform actions that are inherantly slow - such as

[lazyboy, 2016/05/03 01:00:01]

nit: inherently

[Devlin, 2016/05/03 17:03:36]

whoops, done.

+  // anything waiting on user action. As such, we can't always assume that a
+  // long execution time equates to a poorly-performing function.
+  UMA_HISTOGRAM_TIMES("Extensions.Functions.TotalExecutionTime",

[lazyboy, 2016/05/03 01:00:01]

Should we also categorize based on |success|? I'd imagine failed times would be
much smaller than the succeeded ones.

[Devlin, 2016/05/03 17:03:36]

Sounds reasonable.  Done.

+                      timer_.Elapsed());
 }
 
 void ExtensionFunction::OnRespondingLater(ResponseValue value) {