[HTMLImport] Add an Usecounter for the case imported document has stylesheets.

BUG=523952

Review URL: https://codereview.chromium.org/1312733003

git-svn-id: svn://svn.chromium.org/blink/trunk@201301 bbb929c8-8fbe-4397-9dbb-9b2b20218538

third_party/WebKit/Source/core/frame/UseCounter.h

@@ -833,6 +833,7 @@ public:
         CSSAnimationsStackedNeutralKeyframe = 937,
         ReadingCheckedInClickHandler = 938,
         FlexboxIntrinsicSizeAlgorithmIsDifferent = 939,
+        HTMLImportsHasStyleSheets = 940,
 
         // Add new features immediately above this line. Don't change assigned
         // numbers of any item, and don't reuse removed slots.

third_party/WebKit/Source/core/html/imports/HTMLImportChild.cpp

@@ -31,10 +31,12 @@
 #include "config.h"
 #include "core/html/imports/HTMLImportChild.h"
 
+#include "core/css/StyleSheetList.h"
 #include "core/dom/Document.h"
 #include "core/dom/custom/CustomElement.h"
 #include "core/dom/custom/CustomElementMicrotaskImportStep.h"
 #include "core/dom/custom/CustomElementSyncMicrotaskQueue.h"
+#include "core/frame/UseCounter.h"
 #include "core/html/imports/HTMLImportChildClient.h"
 #include "core/html/imports/HTMLImportLoader.h"
 #include "core/html/imports/HTMLImportTreeRoot.h"
@@ -88,6 +90,8 @@ void HTMLImportChild::didFinish()
 void HTMLImportChild::didFinishLoading()
 {
     stateWillChange();
+    if (document() && document()->styleSheets()->length() > 0)
+        UseCounter::count(root()->document(), UseCounter::HTMLImportsHasStyleSheets);
     CustomElement::didFinishLoadingImport(*(root()->document()));
 }