Adds a UMA histogram to monitor omnibox suggest requests.

chrome/browser/autocomplete/search_provider.cc

Index: chrome/browser/autocomplete/search_provider.cc
diff --git a/chrome/browser/autocomplete/search_provider.cc b/chrome/browser/autocomplete/search_provider.cc
index 8bd2c9f2a0b88abb6363c7e3f40a9cf0511330f2..75d7d74dd7d1f927c3bead7f8b8cdf17a47975c9 100644
--- a/chrome/browser/autocomplete/search_provider.cc
+++ b/chrome/browser/autocomplete/search_provider.cc
@@ -293,12 +293,16 @@ void SearchProvider::Run() {
   const TemplateURL* default_url = providers_.GetDefaultProviderURL();
   if (default_url && !default_url->suggestions_url().empty()) {
     suggest_results_pending_++;
+    // Increment bucket 1 in the histogram (number of requests sent).
+    UMA_HISTOGRAM_ENUMERATION("Omnibox.SuggestRequests", 1, 4);
     default_fetcher_.reset(CreateSuggestFetcher(kDefaultProviderURLFetcherID,
         default_url->suggestions_url_ref(), input_.text()));
   }
   const TemplateURL* keyword_url = providers_.GetKeywordProviderURL();
   if (keyword_url && !keyword_url->suggestions_url().empty()) {
     suggest_results_pending_++;
+    // Increment bucket 1 in the histogram (number of requests sent).
+    UMA_HISTOGRAM_ENUMERATION("Omnibox.SuggestRequests", 1, 4);

[Ilya Sherman, 2012/08/15 22:42:06]

To avoid problems from typos and such, there are two best practices for
enumerated histograms:

(1) Only declare the UMA_HISTOGRAM_ENUMERATION macro in a single location for
each distinct histogram.  This usually involves defining a helper function like
LogOmniboxSuggestRequest().  This makes it much harder to name the histogram
differently in different places due to a typo.  (This applies to all histograms,
not just enumerated ones; but many of the other histograms more naturally appear
in just one place in the code.)

(2) Use an actual C++ enumeration to name the constants corresponding to "1" and
"4".  This both helps with readability, makes typos and copy/paste errors more
obvious, and makes it easier to extend the list of enumerated values later
(since you don't have to remember to change the "4" in the macro).

Also, is there any particular reason why you're avoiding use of bucket 0?

[Mark P, 2012/08/15 23:09:46]

Good idea.  Done.
Another good idea.  Done.
I don't like the idea of exploiting the underflow bucket to count things.

     keyword_fetcher_.reset(CreateSuggestFetcher(kKeywordProviderURLFetcherID,
         keyword_url->suggestions_url_ref(), keyword_input_text_));
   }
@@ -332,6 +336,9 @@ void SearchProvider::AddProviderInfo(ProvidersInfo* provider_info) const {
 void SearchProvider::OnURLFetchComplete(const net::URLFetcher* source) {
   DCHECK(!done_);
   suggest_results_pending_--;
+  // Increment bucket 3 in the histogram (number of requests for which
+  // we received a response).
+  UMA_HISTOGRAM_ENUMERATION("Omnibox.SuggestRequests", 3, 4);
   DCHECK_GE(suggest_results_pending_, 0);  // Should never go negative.
   const net::HttpResponseHeaders* const response_headers =
       source->GetResponseHeaders();
@@ -549,6 +556,10 @@ bool SearchProvider::IsQuerySuitableForSuggest() const {
 }
 
 void SearchProvider::StopSuggest() {
+  // Increment bucket 2 in the histogram by the number of requests pending
+  // that were invalidated.
+  for (int i = 0; i < suggest_results_pending_; i++)
+    UMA_HISTOGRAM_ENUMERATION("Omnibox.SuggestRequests", 2, 4);
   suggest_results_pending_ = 0;
   timer_.Stop();
   // Stop any in-progress URL fetches.