DevTools: introduce screencast experiment.

Source/core/inspector/InspectorPageAgent.cpp

Index: Source/core/inspector/InspectorPageAgent.cpp
diff --git a/Source/core/inspector/InspectorPageAgent.cpp b/Source/core/inspector/InspectorPageAgent.cpp
index a428616881b6a40c98b54476055a871c9b22310f..f10f88fd5a675e672dddec4bc6730e4b278ee594 100644
--- a/Source/core/inspector/InspectorPageAgent.cpp
+++ b/Source/core/inspector/InspectorPageAgent.cpp
@@ -1264,7 +1264,17 @@ void InspectorPageAgent::setForceCompositingMode(ErrorString* errorString, bool
     mainFrame->view()->updateCompositingLayersAfterStyleChange();
 }
 
-void InspectorPageAgent::captureScreenshot(ErrorString*, String*)
+void InspectorPageAgent::captureScreenshot(ErrorString*, const String*, const int*, const double*, String*)
+{
+    // Handled on the browser level.
+}
+
+void InspectorPageAgent::startScreencast(ErrorString*, const String*, const int*, const double*)
+{
+    // Handled on the browser level.
+}
+
+void InspectorPageAgent::stopScreencast(ErrorString*)
 {
     // Handled on the browser level.
 }