Add UMA reporting to CdmPromise.

content/renderer/media/cdm_session_adapter.cc

Index: content/renderer/media/cdm_session_adapter.cc
diff --git a/content/renderer/media/cdm_session_adapter.cc b/content/renderer/media/cdm_session_adapter.cc
index 9a84d544c9820abc929dad372dbb02ff74b09bdb..de3d162019f87e75aec7ae36ad9030f0e953a717 100644
--- a/content/renderer/media/cdm_session_adapter.cc
+++ b/content/renderer/media/cdm_session_adapter.cc
@@ -9,6 +9,7 @@
 #include "base/memory/weak_ptr.h"
 #include "base/stl_util.h"
 #include "content/renderer/media/crypto/content_decryption_module_factory.h"
+#include "content/renderer/media/crypto/key_systems.h"
 #include "content/renderer/media/webcontentdecryptionmodulesession_impl.h"
 #include "media/base/cdm_promise.h"
 #include "media/base/media_keys.h"
@@ -16,6 +17,9 @@
 
 namespace content {
 
+const char kMediaEME[] = "Media.EME.";
+const char kDot[] = ".";
+
 CdmSessionAdapter::CdmSessionAdapter() :
 #if defined(ENABLE_BROWSER_CDMS)
     cdm_id_(0),
@@ -32,6 +36,7 @@ bool CdmSessionAdapter::Initialize(
 #endif  // defined(ENABLE_PEPPER_CDMS)
     const std::string& key_system,
     const GURL& security_origin) {
+  key_system_uma_prefix_ = kMediaEME + KeySystemNameForUMA(key_system) + kDot;
   base::WeakPtr<CdmSessionAdapter> weak_this = weak_ptr_factory_.GetWeakPtr();
   media_keys_ = ContentDecryptionModuleFactory::Create(
       key_system,
@@ -103,6 +108,10 @@ media::Decryptor* CdmSessionAdapter::GetDecryptor() {
   return media_keys_->GetDecryptor();
 }
 
+const std::string& CdmSessionAdapter::GetKeySystemUMAPrefix() const {
+  return key_system_uma_prefix_;
+}
+
 #if defined(ENABLE_BROWSER_CDMS)
 int CdmSessionAdapter::GetCdmId() const {
   return cdm_id_;