Add use-counters for use of CSS parsing in WebkitCSSMatrix.

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

Index: third_party/WebKit/Source/core/css/CSSMatrix.cpp
diff --git a/third_party/WebKit/Source/core/css/CSSMatrix.cpp b/third_party/WebKit/Source/core/css/CSSMatrix.cpp
index 00e937709f5d0b396e4f059eed02a216d4d57118..afd86dfca56629cb52a2561f5fdf65d2ec7bd564 100644
--- a/third_party/WebKit/Source/core/css/CSSMatrix.cpp
+++ b/third_party/WebKit/Source/core/css/CSSMatrix.cpp
@@ -46,6 +46,10 @@ CSSMatrix* CSSMatrix::create(ExecutionContext* executionContext,
                              const String& s,
                              ExceptionState& exceptionState) {
   UseCounter::count(executionContext, UseCounter::WebKitCSSMatrix);
+  if (!s.isEmpty()) {
+    UseCounter::count(executionContext,
+                      UseCounter::WebkitCSSMatrixConstructFromString);
+  }
   return new CSSMatrix(s, exceptionState);
 }