Add htm and html to pingable download file types.

chrome/browser/resources/safe_browsing/download_file_types.asciipb

Index: chrome/browser/resources/safe_browsing/download_file_types.asciipb
diff --git a/chrome/browser/resources/safe_browsing/download_file_types.asciipb b/chrome/browser/resources/safe_browsing/download_file_types.asciipb
index 6641e0deac9396623af28db8aa7f1aca74968b8d..bb204b38ce0df8ff214c604169907e0499ba972e 100644
--- a/chrome/browser/resources/safe_browsing/download_file_types.asciipb
+++ b/chrome/browser/resources/safe_browsing/download_file_types.asciipb
@@ -8,7 +8,7 @@
 ##
 ## Top level settings
 ##
-version_id: 9
+version_id: 10
 sampled_ping_probability: 0.01
 default_file_type {
   uma_value: 18
@@ -1808,6 +1808,26 @@ file_types {
     auto_open_hint: DISALLOW_AUTO_OPEN
   }
 }
+file_types {
+  # HTML file.

[Nathan Parker, 2017/05/09 22:00:22]

You could explain that these are used in UwS campaigns via a two-level download
scheme.

And how about adding a crbug link here, so we can easily lookup the rationale? 
Also, file a bug.  :-)

[Jialiu Lin, 2017/05/09 22:13:47]

crbug.com/719784  filed for this CL. :-)
Added more explanation. 

+  extension: "htm"
+  uma_value: 284
+  ping_setting: FULL_PING
+  platform_settings {
+    danger_level: NOT_DANGEROUS
+    auto_open_hint: ALLOW_AUTO_OPEN
+  }
+}
+file_types {
+  # HTML file.
+  extension: "html"
+  uma_value: 285
+  ping_setting: FULL_PING
+  platform_settings {
+    danger_level: NOT_DANGEROUS
+    auto_open_hint: ALLOW_AUTO_OPEN
+  }
+}
 file_types {
   # Hypertext Template File. See https://support.microsoft.com/kb/181689.
   extension: "htt"