Expect InitSegmentReceived() in PipelineIntegrationTest.Encrypted* tests.

This is a follow up of 37e3ddb2, which introduced the InitSegmentReceived()
call.

Since StartPipelineWithEncryptedMedia() also uses MockMediaSource, we should
also expect InitSegmentReceived() to be called. Otherwise, we'll receive
warnings about uninterested mock calls of InitSegmentReceived().

BUG=249428
TEST=This fixes expectations in existing tests.

Review URL: https://codereview.chromium.org/588573003

Cr-Commit-Position: refs/heads/master@{#296099}

media/filters/pipeline_integration_test.cc

@@ -577,6 +577,7 @@ class PipelineIntegrationTest
   void StartPipelineWithEncryptedMedia(
       MockMediaSource* source,
       FakeEncryptedMedia* encrypted_media) {
+    EXPECT_CALL(*source, InitSegmentReceived()).Times(AtLeast(1));
     EXPECT_CALL(*this, OnMetadata(_))
         .Times(AtMost(1))
         .WillRepeatedly(SaveArg<0>(&metadata_));