media: Create MediaCrypto upon MediaDrmBridge creation.

- Create MediaCrypto right after MediaDrmBridge construction or after
  provisioning is successfully completed.
- Do not store mMediaCrypto in Java.

Tests:
- MediaCrypto creation on provisioned device.
- MediaCrypto creation on unprovisioned device with successful provisioning.
- MediaCrypto creation on unprovisioned device with failed provisioning (so null
  MediaCrypto was notified).

BUG=564246
TEST=See above.

Review URL: https://codereview.chromium.org/1540033002

Cr-Commit-Position: refs/heads/master@{#368438}

media/base/android/media_drm_bridge.cc

@@ -292,6 +292,8 @@ scoped_refptr<MediaDrmBridge> MediaDrmBridge::CreateWithoutSessionSupport(
     const std::string& key_system,
     SecurityLevel security_level,
     const CreateFetcherCB& create_fetcher_cb) {
+  DVLOG(1) << __FUNCTION__;
+
   return MediaDrmBridge::Create(key_system, security_level, create_fetcher_cb,
                                 SessionMessageCB(), SessionClosedCB(),
                                 LegacySessionErrorCB(), SessionKeysChangeCB(),
@@ -730,6 +732,7 @@ MediaDrmBridge::MediaDrmBridge(
   ScopedJavaLocalRef<jstring> j_security_level =
       ConvertUTF8ToJavaString(env, security_level_str);
 
+  // Note: OnMediaCryptoReady() could be called in this call.
   j_media_drm_.Reset(Java_MediaDrmBridge_create(
       env, j_scheme_uuid.obj(), j_security_level.obj(),
       reinterpret_cast<intptr_t>(this)));

media/base/android/media_drm_bridge.h

@@ -244,7 +244,8 @@ class MEDIA_EXPORT MediaDrmBridge : public MediaKeys, public PlayerTracker {
 
   // Constructs a MediaDrmBridge for |scheme_uuid| and |security_level|. The
   // default security level will be used if |security_level| is
-  // SECURITY_LEVEL_DEFAULT.
+  // SECURITY_LEVEL_DEFAULT. Sessions should not be created if session callbacks
+  // are null.
   MediaDrmBridge(const std::vector<uint8_t>& scheme_uuid,
                  SecurityLevel security_level,
                  const CreateFetcherCB& create_fetcher_cb,