Add histogram for Blink's spell check request interval

third_party/WebKit/Source/core/editing/spellcheck/SpellCheckRequester.cpp

Index: third_party/WebKit/Source/core/editing/spellcheck/SpellCheckRequester.cpp
diff --git a/third_party/WebKit/Source/core/editing/spellcheck/SpellCheckRequester.cpp b/third_party/WebKit/Source/core/editing/spellcheck/SpellCheckRequester.cpp
index e6f33b1706fda173d0eed478d76ae41fc286d48b..1ab0b971d1ff769da0cfeec239519f229a66471e 100644
--- a/third_party/WebKit/Source/core/editing/spellcheck/SpellCheckRequester.cpp
+++ b/third_party/WebKit/Source/core/editing/spellcheck/SpellCheckRequester.cpp
@@ -34,6 +34,7 @@
 #include "core/frame/LocalFrame.h"
 #include "core/frame/Settings.h"
 #include "core/html/TextControlElement.h"
+#include "platform/Histogram.h"
 #include "platform/text/TextCheckerClient.h"
 
 namespace blink {
@@ -125,6 +126,7 @@ SpellCheckRequester::SpellCheckRequester(LocalFrame& frame)
     : frame_(&frame),
       last_request_sequence_(0),
       last_processed_sequence_(0),
+      last_request_time_(0.0),
       timer_to_process_queued_request_(
           TaskRunnerHelper::Get(TaskType::kUnspecedTimer, &frame),
           this,
@@ -154,6 +156,16 @@ void SpellCheckRequester::RequestCheckingFor(const EphemeralRange& range,
   if (!request)
     return;
 
+  DEFINE_STATIC_LOCAL(CustomCountHistogram,
+                      spell_checker_request_interval_histogram,
+                      ("WebCore.SpellChecker.RequestInterval", 0, 10000, 50));
+  double current_request_time = MonotonicallyIncreasingTime();

[yosin_UTC9, 2017/05/12 04:33:34]

nit: s/double/const double/

[Xiaocheng, 2017/05/12 18:35:14]

Done.

+  if (request_num == 0 && last_request_time_ > 0) {
+    double interval_ms = (current_request_time - last_request_time_) * 1000.0;

[yosin_UTC9, 2017/05/12 04:33:34]

nit: s/double/const double/

[Xiaocheng, 2017/05/12 18:35:14]

Done.

+    spell_checker_request_interval_histogram.Count(interval_ms);
+  }
+  last_request_time_ = current_request_time;
+
   DCHECK_EQ(request->Data().Sequence(), kUnrequestedTextCheckingSequence);
   int sequence = ++last_request_sequence_;
   if (sequence == kUnrequestedTextCheckingSequence)