Record start up latency of DOM distiller viewer

BUG=617701

Review-Url: https://codereview.chromium.org/2011213002
Cr-Commit-Position: refs/heads/master@{#398115}

chrome/browser/dom_distiller/tab_utils.cc

@@ -108,7 +108,8 @@ void SelfDeletingRequestDelegate::TakeViewerHandle(
 void StartNavigationToDistillerViewer(content::WebContents* web_contents,
                                       const GURL& url) {
   GURL viewer_url = dom_distiller::url_utils::GetDistillerViewUrlFromUrl(
-      dom_distiller::kDomDistillerScheme, url);
+      dom_distiller::kDomDistillerScheme, url,
+      (base::TimeTicks::Now() - base::TimeTicks()).InMilliseconds());
   content::NavigationController::LoadURLParams params(viewer_url);
   params.transition_type = ui::PAGE_TRANSITION_AUTO_BOOKMARK;
   web_contents->GetController().LoadURLWithParams(params);

components/dom_distiller/content/browser/dom_distiller_viewer_source.cc

@@ -11,7 +11,7 @@
 
 #include "base/memory/ref_counted_memory.h"
 #include "base/message_loop/message_loop.h"
-#include "base/metrics/user_metrics.h"
+#include "base/metrics/histogram_macros.h"
 #include "base/strings/string_number_conversions.h"
 #include "base/strings/string_util.h"
 #include "base/strings/utf_string_conversions.h"
@@ -157,6 +157,15 @@ void DomDistillerViewerSource::RequestViewerHandle::DidFinishLoad(
     return;
   }
 
+  int64_t start_time_ms = url_utils::GetTimeFromDistillerUrl(validated_url);
+  if (start_time_ms > 0) {
+    base::TimeTicks start_time =
+        base::TimeDelta::FromMilliseconds(start_time_ms) + base::TimeTicks();
+    base::TimeDelta latency = base::TimeTicks::Now() - start_time;
+
+    UMA_HISTOGRAM_TIMES("DomDistiller.Time.ViewerLoading", latency);
+  }
+
   // No SendJavaScript() calls allowed before |buffer_| is run and cleared.
   waiting_for_page_ready_ = false;
   if (!buffer_.empty()) {

components/dom_distiller/core/url_constants.cc

@@ -9,6 +9,7 @@ namespace dom_distiller {
 const char kDomDistillerScheme[] = "chrome-distiller";
 const char kEntryIdKey[] = "entry_id";
 const char kUrlKey[] = "url";
+const char kTimeKey[] = "time";
 const char kViewerCssPath[] = "dom_distiller_viewer.css";
 const char kViewerLoadingImagePath[] = "dom_distiller_material_spinner.svg";
 const char kViewerSaveFontScalingPath[] = "savefontscaling/";

components/dom_distiller/core/url_constants.h

@@ -10,6 +10,7 @@ namespace dom_distiller {
 extern const char kDomDistillerScheme[];
 extern const char kEntryIdKey[];
 extern const char kUrlKey[];
+extern const char kTimeKey[];
 extern const char kViewerCssPath[];
 extern const char kViewerLoadingImagePath[];
 extern const char kViewerSaveFontScalingPath[];

components/dom_distiller/core/url_utils.cc

@@ -7,6 +7,7 @@
 #include <string>
 
 #include "base/guid.h"
+#include "base/strings/string_number_conversions.h"
 #include "components/dom_distiller/core/url_constants.h"
 #include "grit/components_resources.h"
 #include "net/base/url_util.h"
@@ -30,8 +31,13 @@ const GURL GetDistillerViewUrlFromEntryId(const std::string& scheme,
 }
 
 const GURL GetDistillerViewUrlFromUrl(const std::string& scheme,
-                                      const GURL& view_url) {
+                                      const GURL& view_url,
+                                      int64_t start_time_ms) {
   GURL url(scheme + "://" + base::GenerateGUID());
+  if (start_time_ms > 0) {
+    url = net::AppendOrReplaceQueryParameter(url, kTimeKey,
+        base::IntToString(start_time_ms));
+  }
   return net::AppendOrReplaceQueryParameter(url, kUrlKey, view_url.spec());
 }
 
@@ -45,6 +51,21 @@ const GURL GetOriginalUrlFromDistillerUrl(const GURL& url) {
   return GURL(original_url_str);
 }
 
+int64_t GetTimeFromDistillerUrl(const GURL& url) {
+  if (!dom_distiller::url_utils::IsDistilledPage(url))
+    return 0;
+
+  std::string time_str;
+  if (!net::GetValueForKeyInQuery(url, kTimeKey, &time_str))
+    return 0;
+
+  int64_t time_int = 0;
+  if (!base::StringToInt64(time_str, &time_int))
+    return 0;
+
+  return time_int;
+}
+
 std::string GetValueForKeyInUrl(const GURL& url, const std::string& key) {
   if (!url.is_valid())
     return "";

components/dom_distiller/core/url_utils.h

@@ -19,12 +19,17 @@ const GURL GetDistillerViewUrlFromEntryId(const std::string& scheme,
 
 // Returns the URL for viewing distilled content for a URL.
 const GURL GetDistillerViewUrlFromUrl(const std::string& scheme,
-                                      const GURL& view_url);
+                                      const GURL& view_url,
+                                      int64_t start_time_ms = 0);
 
 // Returns the original URL from the distilled URL.
 // If the URL is not distilled, it is returned as is.
 const GURL GetOriginalUrlFromDistillerUrl(const GURL& distilled_url);
 
+// Returns the starting time from the distilled URL.
+// Returns 0 when not available or on error.
+int64_t GetTimeFromDistillerUrl(const GURL& url);
+
 // Returns the value of the query parameter for the given |key| for a given URL.
 // If the URL is invalid or if the key is not found, returns an empty string.
 // If there are multiple keys found in the URL, returns the value for the first

components/dom_distiller/core/url_utils_unittest.cc

@@ -43,7 +43,7 @@ TEST(DomDistillerUrlUtilsTest, TestGetValueForKeyInUrlPathQuery) {
 
 std::string ThroughDistiller(const std::string& url) {
   return GetOriginalUrlFromDistillerUrl(
-      GetDistillerViewUrlFromUrl(kDomDistillerScheme, GURL(url))).spec();
+      GetDistillerViewUrlFromUrl(kDomDistillerScheme, GURL(url), 123)).spec();
 }
 
 std::string GetOriginalUrlFromDistillerUrl(const std::string& url) {

tools/metrics/histograms/histograms.xml

@@ -10079,6 +10079,13 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="DomDistiller.Time.ViewerLoading" units="ms">
+  <owner>wychen@chromium.org</owner>
+  <summary>
+    Records the time from the Reader Mode panel opening to the viewer loaded.
+  </summary>
+</histogram>
+
 <histogram name="DomDistiller.Time.ViewingReaderModePanel" units="ms">
   <owner>mdjones@chromium.org</owner>
   <summary>