Add getCallSiteData to the VM service.

runtime/vm/service/service.idl

Index: runtime/vm/service/service.idl
diff --git a/runtime/vm/service/service.idl b/runtime/vm/service/service.idl
index 0edb79bdc4545889dee824c4226faafb3f4f77c8..f6e1c9fdf7eedaf0026d8080ba89eb7b9fc4568b 100644
--- a/runtime/vm/service/service.idl
+++ b/runtime/vm/service/service.idl
@@ -46,6 +46,9 @@ interface Service {
   // or function.
   getCoverage(isolateId string, targetId string) CodeCoverage
 
+  // Returns call site cache information for a function.
+  getCallSiteData(isolateId string, targetId string) _CallSiteData
+
   // Returns a full cpu profile for an isolate.
   //
   // <code>tagSelector</code> is optional with default 'UserVM'.
@@ -273,6 +276,26 @@ struct CodeCoverage extends Response {
   placeholder int
 }
 
+
+struct _CacheEntry {
+  receiverClass ClassRef
+  count         int
+}
+
+
+struct _CallSite {
+  name         string
+  line         int
+  column       int
+  cacheEntries []_CacheEntry
+}
+
+
+struct _CallSiteData extends Response {
+  function  FunctionRef
+  callSites []_CallSite
+}
+
 // A <code>TagProfile</code> is a limited profile encoded as parallel
 // arrays of tag names and tag values.
 struct TagProfile extends Response {