Lower limit for ZIP analysis to 15MB

The mitigation previously in place for https://crbug.com/919709 isn't
sufficient in preventing long-tail ZIP analysis from taking a long time.
So this CL lowers the size limit for detailed ZIP unpacking. We will
roll this out by a Component Update, then restore to the old limit for
M75.

Bug: 959628
Change-Id: Iae254bfc8cd78aac977f9751c3664407ac6282b0
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1599877Reviewed-by: Varun Khaneja <vakh@chromium.org>
Commit-Queue: Varun Khaneja <vakh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#658342}

chrome/browser/resources/safe_browsing/download_file_types.asciipb

@@ -706,7 +706,7 @@ file_types {
   ping_setting: FULL_PING
   inspection_type: ZIP
   platform_settings {
-    max_file_size_to_analyze: 52428800 # 50MB
+    max_file_size_to_analyze: 15728640 # 15MB
   }
 }
 file_types {