Use the right ref count macros for base::Bind call

chrome/browser/android/cdm/media_drm_credential_manager.cc sent
a g_browser_process->system_request_context() into a Bind call
without using any ref counting macros. That is prohibited by the
bind system but the code got away with it when the pointer
was just forward declared so that Bind didn't know that it was
a ref counted type.

In jumbo builds the compiler knew more about the return type of
g_browser_process->system_request_context() and failed to compile
because of static_asserts in bind_internal.h.

This patch adds base::Unretained() since that seems to be the
right macro for this type of value.

Bug: 746957
Change-Id: Idfc3ad9bd6708dbc5ef4f295397d05d961595b4a
Reviewed-on: https://chromium-review.googlesource.com/897535Reviewed-by: Chrome Cunningham <chcunningham@chromium.org>
Reviewed-by: Xiaohan Wang <xhwang@chromium.org>
Commit-Queue: Daniel Bratell <bratell@opera.com>
Cr-Commit-Position: refs/heads/master@{#533839}

chrome/browser/media/android/cdm/media_drm_credential_manager.cc

@@ -92,7 +92,7 @@ void MediaDrmCredentialManager::ResetCredentialsInternal(
   // Create provision fetcher for the default browser http request context.
   media::CreateFetcherCB create_fetcher_cb =
       base::Bind(&content::CreateProvisionFetcher,
-                 g_browser_process->system_request_context());
+                 base::Unretained(g_browser_process->system_request_context()));
 
   ResetCredentialsCB reset_credentials_cb =
       base::Bind(&MediaDrmCredentialManager::OnResetCredentialsCompleted,