Implement LoadSession() for EME

In preparation for MediaKeySession.load(), add support for load()
on the Chromium side.

BUG=338831
TEST=existing EME tests still pass (new tests coming once implemented)

Review URL: https://codereview.chromium.org/639473004

Cr-Commit-Position: refs/heads/master@{#298798}

content/renderer/media/cdm_session_adapter.cc

@@ -99,6 +99,12 @@ void CdmSessionAdapter::InitializeNewSession(
                              promise.Pass());
 }
 
+void CdmSessionAdapter::LoadSession(
+    const std::string& web_session_id,
+    scoped_ptr<media::NewSessionCdmPromise> promise) {
+  media_keys_->LoadSession(web_session_id, promise.Pass());
+}
+
 void CdmSessionAdapter::UpdateSession(
     const std::string& web_session_id,
     const uint8* response,

content/renderer/media/cdm_session_adapter.h

@@ -76,6 +76,10 @@ class CdmSessionAdapter : public base::RefCounted<CdmSessionAdapter> {
                             media::MediaKeys::SessionType session_type,
                             scoped_ptr<media::NewSessionCdmPromise> promise);
 
+  // Loads the session specified by |web_session_id|.
+  void LoadSession(const std::string& web_session_id,
+                   scoped_ptr<media::NewSessionCdmPromise> promise);
+
   // Updates the session specified by |web_session_id| with |response|.
   void UpdateSession(const std::string& web_session_id,
                      const uint8* response,

content/renderer/media/webcontentdecryptionmodulesession_impl.cc

@@ -17,6 +17,7 @@
 namespace content {
 
 const char kCreateSessionUMAName[] = "CreateSession";
+const char kLoadSessionUMAName[] = "LoadSession";
 
 WebContentDecryptionModuleSessionImpl::WebContentDecryptionModuleSessionImpl(
     const scoped_refptr<CdmSessionAdapter>& adapter)
@@ -64,6 +65,7 @@ void WebContentDecryptionModuleSessionImpl::initializeNewSession(
     size_t init_data_length,
     const blink::WebString& session_type,
     blink::WebContentDecryptionModuleResult result) {
+  DCHECK(web_session_id_.empty());
 
   // TODO(ddorwin): Guard against this in supported types check and remove this.
   // Chromium only supports ASCII MIME types.
@@ -97,6 +99,22 @@ void WebContentDecryptionModuleSessionImpl::initializeNewSession(
               base::Unretained(this)))));
 }
 
+void WebContentDecryptionModuleSessionImpl::load(
+    const blink::WebString& session_id,
+    blink::WebContentDecryptionModuleResult result) {
+  DCHECK(!session_id.isEmpty());
+  DCHECK(web_session_id_.empty());
+
+  adapter_->LoadSession(
+      base::UTF16ToASCII(session_id),
+      scoped_ptr<media::NewSessionCdmPromise>(new NewSessionCdmResultPromise(
+          result,
+          adapter_->GetKeySystemUMAPrefix() + kLoadSessionUMAName,
+          base::Bind(
+              &WebContentDecryptionModuleSessionImpl::OnSessionInitialized,
+              base::Unretained(this)))));
+}
+
 void WebContentDecryptionModuleSessionImpl::update(
     const uint8* response,
     size_t response_length,

content/renderer/media/webcontentdecryptionmodulesession_impl.h

@@ -46,6 +46,8 @@ class WebContentDecryptionModuleSessionImpl
       size_t init_data_length,
       const blink::WebString& session_type,
       blink::WebContentDecryptionModuleResult result);
+  virtual void load(const blink::WebString& session_id,
+                    blink::WebContentDecryptionModuleResult result);
   virtual void update(const uint8* response,
                       size_t response_length,
                       blink::WebContentDecryptionModuleResult result);

tools/metrics/histograms/histograms.xml

@@ -11678,6 +11678,13 @@ Therefore, the affected-histogram name has to have at least one dot in it.
   <summary>KeyError event count using the Clear Key key system.</summary>
 </histogram>
 
+<histogram name="Media.EME.ClearKey.LoadSession" enum="CdmPromiseResult">
+  <owner>sandersd@chromium.org</owner>
+  <summary>
+    Result of Clear Key loadSession promises handled by Chromium code.
+  </summary>
+</histogram>
+
 <histogram name="Media.EME.NeedKey">
   <owner>xhwang@chromium.org</owner>
   <summary>EME NeedKey event count.</summary>
@@ -11729,6 +11736,14 @@ Therefore, the affected-histogram name has to have at least one dot in it.
   <summary>KeyError event count using an unknown key system.</summary>
 </histogram>
 
+<histogram name="Media.EME.Unknown.LoadSession" enum="CdmPromiseResult">
+  <owner>sandersd@chromium.org</owner>
+  <summary>
+    Result of loadSession promises for unknown key systems promises that were
+    handled by Chromium code.
+  </summary>
+</histogram>
+
 <histogram name="Media.EME.Unknown.SystemCode" units="system code">
   <owner>xhwang@chromium.org</owner>
   <summary>System code count using an unknown key system.</summary>
@@ -11772,6 +11787,13 @@ Therefore, the affected-histogram name has to have at least one dot in it.
   <summary>KeyError event count using the Widevine key system.</summary>
 </histogram>
 
+<histogram name="Media.EME.Widevine.LoadSession" enum="CdmPromiseResult">
+  <owner>sandersd@chromium.org</owner>
+  <summary>
+    Result of Widevine loadSession promises handled by Chromium code.
+  </summary>
+</histogram>
+
 <histogram name="Media.EME.Widevine.SystemCode" units="system code">
   <owner>xhwang@chromium.org</owner>
   <summary>System code count using the Widevine key system.</summary>