Add UMA histogram DomDistiller.Time.RunJavaScript

This measures time spent in ExecuteJavaScript() in DomDistiller. It
includes JavaScript code transmission through IPC, parsing, compilation,
execution, and returning the JSON back through IPC.

We already have DomDistiller.Time.DistillationTotal, but it is measured
within JavaScript.

In DomDistiller.Time.*, DistillationTotal < RunJavaScript < DistillPage.

BUG=497430

Review URL: https://codereview.chromium.org/1143173009

Cr-Commit-Position: refs/heads/master@{#333670}

components/dom_distiller/content/distiller_page_web_contents.cc

@@ -6,6 +6,7 @@
 
 #include "base/callback.h"
 #include "base/memory/scoped_ptr.h"
+#include "base/metrics/histogram.h"
 #include "base/strings/utf_string_conversions.h"
 #include "components/dom_distiller/content/web_contents_main_frame_observer.h"
 #include "components/dom_distiller/core/distiller_page.h"
@@ -164,7 +165,7 @@ void DistillerPageWebContents::DidFailLoad(
     DCHECK(state_ == LOADING_PAGE || state_ == EXECUTING_JAVASCRIPT);
     state_ = PAGELOAD_FAILED;
     scoped_ptr<base::Value> empty = base::Value::CreateNullValue();
-    OnWebContentsDistillationDone(GURL(), empty.get());
+    OnWebContentsDistillationDone(GURL(), base::TimeTicks(), empty.get());
   }
 }
 
@@ -183,15 +184,24 @@ void DistillerPageWebContents::ExecuteJavaScript() {
       base::UTF8ToUTF16(script_),
       base::Bind(&DistillerPageWebContents::OnWebContentsDistillationDone,
                  base::Unretained(this),
-                 source_page_handle_->web_contents()->GetLastCommittedURL()));
+                 source_page_handle_->web_contents()->GetLastCommittedURL(),
+                 base::TimeTicks::Now()));
 }
 
 void DistillerPageWebContents::OnWebContentsDistillationDone(
     const GURL& page_url,
+    const base::TimeTicks& javascript_start,
     const base::Value* value) {
   DCHECK(state_ == IDLE || state_ == LOADING_PAGE ||  // TODO(nyquist): 493795.
          state_ == PAGELOAD_FAILED || state_ == EXECUTING_JAVASCRIPT);
   state_ = IDLE;
+
+  if (!javascript_start.is_null()) {
+    base::TimeDelta javascript_time = base::TimeTicks::Now() - javascript_start;
+    UMA_HISTOGRAM_TIMES("DomDistiller.Time.RunJavaScript", javascript_time);
+    DVLOG(1) << "DomDistiller.Time.RunJavaScript = " << javascript_time;
+  }
+
   DistillerPage::OnDistillationDone(page_url, value);
 }
 

components/dom_distiller/content/distiller_page_web_contents.h

@@ -100,6 +100,7 @@ class DistillerPageWebContents : public DistillerPage,
 
   // Called when the distillation is done or if the page load failed.
   void OnWebContentsDistillationDone(const GURL& page_url,
+                                     const base::TimeTicks& javascript_start,
                                      const base::Value* value);
 
   // The current state of the |DistillerPage|, initially |IDLE|.

tools/metrics/histograms/histograms.xml

@@ -6507,6 +6507,15 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="DomDistiller.Time.RunJavaScript" units="milliseconds">
+  <owner>wychen@chromium.org</owner>
+  <summary>
+    Time spent in ExecuteJavaScript() in DomDistiller. It includes JavaScript
+    code transmission through IPC, parsing, compilation, execution, and
+    returning the JSON back through IPC.
+  </summary>
+</histogram>
+
 <histogram name="DomDistiller.Time.SwipeToPaint" units="milliseconds">
   <owner>wychen@chromium.org</owner>
   <summary>