add a download slices table into history download db

components/history/core/browser/download_database.h

Index: components/history/core/browser/download_database.h
diff --git a/components/history/core/browser/download_database.h b/components/history/core/browser/download_database.h
index 6388195eccf2b1b0f314fe86c21487ce10a6fd21..25d07d91d3edadddffb2c61370299a3dac4d8986 100644
--- a/components/history/core/browser/download_database.h
+++ b/components/history/core/browser/download_database.h
@@ -8,6 +8,7 @@
 #include <stddef.h>
 #include <stdint.h>
 
+#include <map>
 #include <string>
 #include <vector>
 
@@ -22,6 +23,7 @@ class Connection;
 
 namespace history {
 
+struct DownloadJobInfo;
 struct DownloadRow;
 
 // Maintains a table of downloads.
@@ -113,6 +115,20 @@ class DownloadDatabase {
 
   void RemoveDownloadURLs(uint32_t id);
 
+  // Creates a new download job. Returns true on success, or false otherwise.
+  bool CreateDownloadJob(const DownloadJobInfo& info);
+
+  // Updates the state of a download job. Returns true on success, or false
+  // if the job doesn't exists..
+  bool UpdateDownloadJob(const DownloadJobInfo& info);
+
+  // Delete all the download jobs associated with one DownloadRow.
+  void RemoveDownloadJobs(uint32_t id);

[Scott Hess - ex-Googler, 2017/02/06 21:22:16]

Seems like this should be DownloadId.

[qinmin, 2017/02/06 23:39:22]

Done.

+
+  // Helper method to query the download jobs for all the records in
+  // |download_row_map|.
+  void QueryDownloadJobs(std::map<uint32_t, DownloadRow*>* download_row_map);

[Scott Hess - ex-Googler, 2017/02/06 21:22:16]

This too.

Also, you should be able to return a map<>, right?  Though I haven't dug around
related code to see if that's the style in these parts.

[qinmin, 2017/02/06 23:39:22]

Done changing it to DownloadId. For the return values, we have a "void
QueryDownloads(std::vector<DownloadRow>* results)" at the top of this file, so i
think it is ok to use the input param for output. This is also more efficient
than making a new map as output.

+
   bool owning_thread_set_;
   base::PlatformThreadId owning_thread_;