Measure usage of createObjectURL and srcObject

third_party/WebKit/Source/modules/mediasource/URLMediaSource.cpp

Index: third_party/WebKit/Source/modules/mediasource/URLMediaSource.cpp
diff --git a/third_party/WebKit/Source/modules/mediasource/URLMediaSource.cpp b/third_party/WebKit/Source/modules/mediasource/URLMediaSource.cpp
index b5f232dcc1ca8415c5c4c3861e4e5c40cce8f3f1..cfa8aec10a67b1c250edbffc5e773c6b98d046f9 100644
--- a/third_party/WebKit/Source/modules/mediasource/URLMediaSource.cpp
+++ b/third_party/WebKit/Source/modules/mediasource/URLMediaSource.cpp
@@ -31,6 +31,7 @@
 #include "modules/mediasource/URLMediaSource.h"
 
 #include "core/dom/DOMURL.h"
+#include "core/frame/UseCounter.h"
 #include "modules/mediasource/MediaSource.h"
 
 namespace blink {
@@ -39,9 +40,10 @@ String URLMediaSource::createObjectURL(ExecutionContext* executionContext, Media
 {
     // Since WebWorkers cannot obtain MediaSource objects, we should be on the main thread.
     DCHECK(isMainThread());
+    DCHECK(executionContext);

[hta - Chromium, 2016/09/29 13:46:33]

Since you're now DCHECKing (and, I think, crashing in production) something that
used to return an empty string, this needs review to figure out if it matters.

[foolip, 2016/09/29 14:54:45]

executionContext and source cannot be null here, as in
URLFileAPI::createObjectURL.

+    DCHECK(source);
 
-    if (!executionContext)
-        return String();
+    UseCounter::count(executionContext, UseCounter::CreateObjectURLMediaSource);
     return DOMURL::createPublicURL(executionContext, source);
 }