ServiceWorker: UMA histogram to track the size of Service Worker scripts

Source/web/WebEmbeddedWorkerImpl.cpp

Index: Source/web/WebEmbeddedWorkerImpl.cpp
diff --git a/Source/web/WebEmbeddedWorkerImpl.cpp b/Source/web/WebEmbeddedWorkerImpl.cpp
index 3551982582d32687f2d732f2a22b536f6cbab494..a9b82e734e3fb8a5a0780503e83aa88f07a42d4e 100644
--- a/Source/web/WebEmbeddedWorkerImpl.cpp
+++ b/Source/web/WebEmbeddedWorkerImpl.cpp
@@ -50,6 +50,7 @@
 #include "platform/SharedBuffer.h"
 #include "platform/heap/Handle.h"
 #include "platform/network/ContentSecurityPolicyParsers.h"
+#include "public/platform/Platform.h"
 #include "public/platform/WebURLRequest.h"
 #include "public/web/WebDevToolsAgent.h"
 #include "public/web/WebServiceWorkerContextClient.h"
@@ -380,6 +381,8 @@ void WebEmbeddedWorkerImpl::onScriptLoaderFinished()
         return;
     }
 
+    Platform::current()->histogramCustomCounts("ServiceWorker.ScriptSize", m_mainScriptLoader->script().length(), 1000, 5000000, 50);
+
     if (m_pauseAfterDownloadState == DoPauseAfterDownload) {
         m_pauseAfterDownloadState = IsPausedAfterDownload;
         m_workerContextClient->didPauseAfterDownload();