Add CSSTiming to collect aggregate PLT-level stats about CSS.

third_party/WebKit/Source/core/css/StyleSheetContents.cpp

Index: third_party/WebKit/Source/core/css/StyleSheetContents.cpp
diff --git a/third_party/WebKit/Source/core/css/StyleSheetContents.cpp b/third_party/WebKit/Source/core/css/StyleSheetContents.cpp
index 0e6397fa873fbed6093505d54431650d9a884b2d..2846ab8102df2ed76caa55847fe8d0aa51fb1c4f 100644
--- a/third_party/WebKit/Source/core/css/StyleSheetContents.cpp
+++ b/third_party/WebKit/Source/core/css/StyleSheetContents.cpp
@@ -21,6 +21,7 @@
 #include "core/css/StyleSheetContents.h"
 
 #include "core/css/CSSStyleSheet.h"
+#include "core/css/CSSTiming.h"
 #include "core/css/StylePropertySet.h"
 #include "core/css/StyleRule.h"
 #include "core/css/StyleRuleImport.h"
@@ -327,7 +328,7 @@ void StyleSheetContents::parseAuthorStyleSheet(
     const SecurityOrigin* securityOrigin) {
   TRACE_EVENT1("blink,devtools.timeline", "ParseAuthorStyleSheet", "data",
                InspectorParseAuthorStyleSheetEvent::data(cachedStyleSheet));
-  SCOPED_BLINK_UMA_HISTOGRAM_TIMER("Style.AuthorStyleSheet.ParseTime");
+  double startTime = monotonicallyIncreasingTimeMS();

[Bryan McQuade, 2016/11/04 14:11:30]

can we call this startTimeMs? any time we're dealing with double rather than a
well typed class like TimeDelta we should declare the units in the name to
minimize chance for bugs. i'm also not sure we need to convert to millis here.
though i'm not an expert when it comes to doubles, my sense is that they can
meet our needs here with second resolution.

[Charlie Harrison, 2016/11/04 16:05:19]

Changed the name. Note that our local histogram here expects microseconds.

 
   bool isSameOriginRequest =
       securityOrigin && securityOrigin->canRequest(baseURL());
@@ -360,6 +361,14 @@ void StyleSheetContents::parseAuthorStyleSheet(
   CSSParserContext context(parserContext(), UseCounter::getFrom(this));
   CSSParser::parseSheet(context, this, sheetText,
                         RuntimeEnabledFeatures::lazyParseCSSEnabled());
+
+  DEFINE_STATIC_LOCAL(CustomCountHistogram, parseHistogram,
+                      ("Style.AuthorStyleSheet.ParseTime", 0, 10000000, 50));
+  double parseDuration = 1000 * (monotonicallyIncreasingTimeMS() - startTime);
+  parseHistogram.count(parseDuration);
+  if (Document* document = singleOwnerDocument()) {
+    CSSTiming::from(*document).recordAuthorStyleSheetParseTime(parseDuration);
+  }
 }
 
 void StyleSheetContents::parseString(const String& sheetText) {