Move logic of recording main thread scrolling reasons from cc to blink::ScrollManager

cc/input/main_thread_scrolling_reason.h

Index: cc/input/main_thread_scrolling_reason.h
diff --git a/cc/input/main_thread_scrolling_reason.h b/cc/input/main_thread_scrolling_reason.h
index 9746d9425740d96ff63e52707b498f08b4878d80..526bc1d826275f81d68b52112ee8035c3d1bed78 100644
--- a/cc/input/main_thread_scrolling_reason.h
+++ b/cc/input/main_thread_scrolling_reason.h
@@ -148,20 +148,6 @@ struct MainThreadScrollingReason {
       tracedValue->AppendString("Page-based scrolling");
     tracedValue->EndArray();
   }
-
-  // For a given reason, return its index in enum
-  static int getReasonIndex(uint32_t reason) {
-    // Multiple reasons provided
-    if (reason & (reason - 1))
-      return -1;
-
-    int index = -1;
-    while (reason > 0) {
-      reason = reason >> 1;
-      ++index;
-    }
-    return index;
-  }
 };
 
 }  // namespace cc