Extensions: Add metrics for Web Request API actions.

extensions/browser/api/web_request/web_request_api.cc

Index: extensions/browser/api/web_request/web_request_api.cc
diff --git a/extensions/browser/api/web_request/web_request_api.cc b/extensions/browser/api/web_request/web_request_api.cc
index b81023248535d3064adaf563327f06568d444b64..0c3fb78717d20ac09b539d4cc93826101816c520 100644
--- a/extensions/browser/api/web_request/web_request_api.cc
+++ b/extensions/browser/api/web_request/web_request_api.cc
@@ -87,7 +87,21 @@ namespace web_request = api::web_request;
 
 namespace {
 
+// Describes the action taken by the Web Request API for a given stage of a web
+// request.
+// These values are written to logs.  New enum values can be added, but existing
+// enum values must never be renumbered or deleted and reused.
+enum RequestAction {
+  CANCEL = 0,
+  REDIRECT = 1,
+  MODIFY_REQUEST_HEADERS = 2,
+  MODIFY_RESPONSE_HEADERS = 3,
+  SET_AUTH_CREDENTIALS = 4,
+  MAX
+};
+
 const char kWebRequestEventPrefix[] = "webRequest.";
+const char kWebRequestActionUMA[] = "Extensions.WebRequestAction";
 
 // List of all the webRequest events.
 const char* const kWebRequestEvents[] = {
@@ -1800,6 +1814,8 @@ int ExtensionWebRequestEventRouter::ExecuteDeltas(
       base::Time::Now() - blocked_request.blocking_time;
   request_time_tracker_->IncrementTotalBlockTime(request_id, block_time);
 
+  bool request_headers_modified = false;
+  bool response_headers_modified = false;
   bool credentials_set = false;
 
   deltas.sort(&helpers::InDecreasingExtensionInstallationTimeOrder);
@@ -1817,17 +1833,15 @@ int ExtensionWebRequestEventRouter::ExecuteDeltas(
   } else if (blocked_request.event == kOnBeforeSendHeaders) {
     CHECK(!blocked_request.callback.is_null());
     helpers::MergeOnBeforeSendHeadersResponses(
-        blocked_request.response_deltas,
-        blocked_request.request_headers,
-        &warnings,
-        blocked_request.net_log);
+        blocked_request.response_deltas, blocked_request.request_headers,
+        &warnings, blocked_request.net_log, &request_headers_modified);
   } else if (blocked_request.event == kOnHeadersReceived) {
     CHECK(!blocked_request.callback.is_null());
     helpers::MergeOnHeadersReceivedResponses(
         blocked_request.request->url(), blocked_request.response_deltas,
         blocked_request.original_response_headers.get(),
         blocked_request.override_response_headers, blocked_request.new_url,
-        &warnings, blocked_request.net_log);
+        &warnings, blocked_request.net_log, &response_headers_modified);
   } else if (blocked_request.event == kOnAuthRequired) {
     CHECK(blocked_request.callback.is_null());
     CHECK(!blocked_request.auth_callback.is_null());
@@ -1850,11 +1864,39 @@ int ExtensionWebRequestEventRouter::ExecuteDeltas(
                    browser_context, warnings));
   }
 
-  if (canceled) {
+  const bool redirected =
+      blocked_request.new_url && !blocked_request.new_url->is_empty();
+
+  if (canceled)
     request_time_tracker_->SetRequestCanceled(request_id);
-  } else if (blocked_request.new_url &&
-             !blocked_request.new_url->is_empty()) {
+  else if (redirected)
     request_time_tracker_->SetRequestRedirected(request_id);
+
+  // Log UMA metrics. Note: We are not necessarily concerned with the final
+  // action taken. Instead we are interested in how frequently the different
+  // actions are used by extensions.

[Devlin, 2017/02/25 18:39:34]

nit: Might be worth explicitly calling out that multiple actions can be taken in
a single delta execution.

[karandeepb, 2017/02/28 00:56:45]

Done.

+  if (canceled) {
+    UMA_HISTOGRAM_ENUMERATION(kWebRequestActionUMA, RequestAction::CANCEL,
+                              RequestAction::MAX);

[Ilya Sherman, 2017/02/27 19:29:25]

Please create a wrapper for emitting to this histogram, so that there's only a
single UMA_HISTOGRAM_ENUMERATION call for it.  The macro expands to a fair bit
of code, so it's helpful for that expansion to only happen once per histogram.

[karandeepb, 2017/02/28 00:56:45]

Done.

+  }
+  if (redirected) {
+    UMA_HISTOGRAM_ENUMERATION(kWebRequestActionUMA, RequestAction::REDIRECT,
+                              RequestAction::MAX);
+  }
+  if (request_headers_modified) {
+    UMA_HISTOGRAM_ENUMERATION(kWebRequestActionUMA,
+                              RequestAction::MODIFY_REQUEST_HEADERS,
+                              RequestAction::MAX);
+  }
+  if (response_headers_modified) {
+    UMA_HISTOGRAM_ENUMERATION(kWebRequestActionUMA,
+                              RequestAction::MODIFY_RESPONSE_HEADERS,
+                              RequestAction::MAX);
+  }
+  if (credentials_set) {
+    UMA_HISTOGRAM_ENUMERATION(kWebRequestActionUMA,
+                              RequestAction::SET_AUTH_CREDENTIALS,
+                              RequestAction::MAX);
   }
 
   // This triggers onErrorOccurred if canceled is true.