Allow DownloadManagerImpl to get InProgressDownloadManager from DownloadManagerService

InProgressDownloadManager could get created before DownloadManagerImpl ctor.
And DownloadManagerService will own the InProgressDownloadManager in that case.
This CL allows DownloadManagerImpl to retrieve the pre-created
InProgressDownloadManager from DownloadManagerService

BUG=695115

Change-Id: Ie2d553894e623116a5e09ae54ec4b8672b180c7f
Reviewed-on: https://chromium-review.googlesource.com/1135986
Commit-Queue: Min Qin <[email protected]>
Reviewed-by: Xing Liu <[email protected]>
Reviewed-by: John Abd-El-Malek <[email protected]>
Cr-Commit-Position: refs/heads/master@{#577075}
diff --git a/content/browser/browser_context.cc b/content/browser/browser_context.cc
index 199a676..0ff903d 100644
--- a/content/browser/browser_context.cc
+++ b/content/browser/browser_context.cc
@@ -694,4 +694,9 @@
   return decode_history;
 }
 
+download::InProgressDownloadManager*
+BrowserContext::RetriveInProgressDownloadManager() {
+  return nullptr;
+}
+
 }  // namespace content