Add metrics for coalesced permission prompts.

chrome/browser/permissions/permission_uma_util.cc

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "chrome/browser/permissions/permission_uma_util.h"
 
 #include <utility>
 
 #include "base/metrics/histogram_macros.h"
 #include "base/strings/stringprintf.h"
@@ skipping 268 matching lines @@
 void PermissionUmaUtil::PermissionPromptShown(
     const std::vector<PermissionBubbleRequest*>& requests) {
   DCHECK(!requests.empty());
   PermissionBubbleType permission_prompt_type = PermissionBubbleType::MULTIPLE;
   if (requests.size() == 1)
     permission_prompt_type = requests[0]->GetPermissionBubbleType();
   UMA_HISTOGRAM_ENUMERATION(
       "Permissions.Prompt.Shown",
       static_cast<base::HistogramBase::Sample>(permission_prompt_type),
       static_cast<base::HistogramBase::Sample>(PermissionBubbleType::NUM));
+
+  UMA_HISTOGRAM_ENUMERATION(
+      "Permissions.Prompt.RequestsPerPrompt",
+      static_cast<base::HistogramBase::Sample>(requests.size()),
+      static_cast<base::HistogramBase::Sample>(10));
+
+  if (requests.size() > 1) {
+    for (const auto* request : requests) {
+      UMA_HISTOGRAM_ENUMERATION(
+          "Permissions.Prompt.MergedBubbleTypes",
+          static_cast<base::HistogramBase::Sample>(
+              request->GetPermissionBubbleType()),

[felt, 2016/04/28 23:55:19]

i am wondering, how do you plan to interpret this? if we end up with a histogram
full of camera, mic, and geolocation, we still won't know which of them are
being requested together right?

[benwells, 2016/04/29 00:07:51]

That's right. We'd know that camera, mic and geo often get merged into other
things, but not what they get merged into.

We could explode out the combinations we report into one histogram enum:
mic+camera
mic+geo
camera+geo
mic+camera+geo

But I thought that seemed pretty complicated and I'm not sure its worth it.

[felt, 2016/04/29 00:19:43]

if you are looking for specific combinations (like mic+camera) you could
specifically histogram those instead of everything. (actually my honest guess is
this will all be mic+camera anyway.)

+          static_cast<base::HistogramBase::Sample>(PermissionBubbleType::NUM));
+    }
+  }
 }