android: create cache dir if needed.

When using a subdirectory of the Android cache dir (e.g. in WebView),
explicitly create the directory in PathUtils instead of relying on any
user of the directory creating it implicitly.

Set the directory mode to 02700 which is what it currently gets set to
when created implicitly.

Fixed: 963640
Change-Id: I8e1c140241d6a2decfcd27186b767ef05e7a4320
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2432447Reviewed-by: Anna Malova <amalova@chromium.org>
Commit-Queue: Richard Coles <torne@chromium.org>
Cr-Commit-Position: refs/heads/master@{#811257}

base/android/java/src/org/chromium/base/PathUtils.java

@@ -108,8 +108,11 @@ public abstract class PathUtils {
             if (sCacheSubDirectory == null) {
                 paths[CACHE_DIRECTORY] = appContext.getCacheDir().getPath();
             } else {
-                paths[CACHE_DIRECTORY] =
-                        new File(appContext.getCacheDir(), sCacheSubDirectory).getPath();
+                File cacheDir = new File(appContext.getCacheDir(), sCacheSubDirectory);
+                assert cacheDir.mkdir();
+                paths[CACHE_DIRECTORY] = cacheDir.getPath();
+                // Set to rwx--S--- as the Android cache dir has a distinct gid and is setgid.
+                chmod(paths[CACHE_DIRECTORY], 02700);
             }
         }
         return paths;