Don't auto-own the tpm on the first Chromium boot.

For Chromium builds, instead of triggering tpm ownership on boot,
rely on it being triggered after the first login (as it was before
CL:688763).

after booting, (b) the tpm is owned after logging in.

Bug: 799664
Test: clear the owner, reboot, verify that (a) the tpm is not owned
Change-Id: I991333e0f049c998dc126827dc141419bf1c3503
Reviewed-on: https://chromium-review.googlesource.com/917537Reviewed-by: Alexander Alekseev <alemate@chromium.org>
Commit-Queue: Andrey Pronin <apronin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#536764}

chrome/browser/chromeos/chrome_browser_main_chromeos.cc

@@ -251,15 +251,18 @@ void GetSystemSlotOnIOThread(
   }
 }
 
-// Verifies if shall signal to the platform that it can attempt owning
-// the tpm. This signal is sent on every boot after it has been initially
-// allowed by accepting EULA to make sure we are not stuck in interrupted
-// tpm initialization state.
+// Decides if on start we shall signal to the platform that it can attempt
+// owning the TPM.
+// For official Chrome builds, send this signal if EULA has been accepted
+// already (i.e. the user has started OOBE) to make sure we are not stuck with
+// uninitialized TPM after an interrupted OOBE process.
+// For Chromium builds, don't send it here. Instead, rely on this signal being
+// sent after each successful login.
 bool ShallAttemptTpmOwnership() {
 #if defined(GOOGLE_CHROME_BUILD)
   return StartupUtils::IsEulaAccepted();
 #else
-  return true;
+  return false;
 #endif
 }