Change most uses of Pickle to base::Pickle

There should be no behavior change.

TBR=jschuh (IPC messages)

Review URL: https://codereview.chromium.org/1154283003

Cr-Commit-Position: refs/heads/master@{#332552}
diff --git a/net/cert/signed_certificate_timestamp_unittest.cc b/net/cert/signed_certificate_timestamp_unittest.cc
index 79f4621..90b4ab74 100644
--- a/net/cert/signed_certificate_timestamp_unittest.cc
+++ b/net/cert/signed_certificate_timestamp_unittest.cc
@@ -31,10 +31,10 @@
 };
 
 TEST_F(SignedCertificateTimestampTest, PicklesAndUnpickles) {
-  Pickle pickle;
+  base::Pickle pickle;
 
   sample_sct_->Persist(&pickle);
-  PickleIterator iter(pickle);
+  base::PickleIterator iter(pickle);
 
   scoped_refptr<SignedCertificateTimestamp> unpickled_sct(
       SignedCertificateTimestamp::CreateFromPickle(&iter));