Revert of Pre-cache downloads directory path in PathUtils. (patchset #1 id:1 of https://codereview.chromium.org/1281273003/ )

Reason for revert:
Revert because it breaks new beta. See
https://code.google.com/p/chromium/issues/detail?id=528377

Original issue's description:
> Pre-cache downloads directory path in PathUtils.
>
> When Chrome tabs are swiped away and user starts Chrome again,
> their default downloads directory is requested. This causes a
> StrictMode policy violation since it results in a ~60ms disk
> read. Thus by adding this call to the initial AsyncTask we
> save that time when the directory is requested by native.
>
> This must only be called in the browser process as the sandbox
> processes do not need to make the call nor can they make the
> call(results in NPE).
>
> BUG=508615
>
> Committed: https://crrev.com/4a7568dffab924d3710a68949dca0717bdad3352
> Cr-Commit-Position: refs/heads/master@{#342672}

[email protected], [email protected]
[email protected], [email protected], [email protected]
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=508615

Review URL: https://codereview.chromium.org/1328043002

Cr-Commit-Position: refs/heads/master@{#347518}

Review URL: https://codereview.chromium.org/1315443012 .

Cr-Commit-Position: refs/branch-heads/2490@{#186}
Cr-Branched-From: 7790a35-refs/heads/master@{#344925}

Author: Daniel Sievers

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

@@ -23,8 +23,7 @@ public abstract class PathUtils {
     private static final int DATA_DIRECTORY = 0;
     private static final int DATABASE_DIRECTORY = 1;
     private static final int CACHE_DIRECTORY = 2;
-    private static final int DOWNLOADS_DIRECTORY = 3;
-    private static final int NUM_DIRECTORIES = 4;
+    private static final int NUM_DIRECTORIES = 3;
     private static AsyncTask<String, Void, String[]> sDirPathFetchTask;
 
     private static File sThumbnailDirectory;
@@ -50,10 +49,7 @@ protected String[] doInBackground(String... dataDirectorySuffix) {
                 paths[DATABASE_DIRECTORY] = appContext.getDatabasePath("foo").getParent();
                 // TODO(wnwen): Find a way to avoid calling this function in renderer process.
                 if (appContext.getCacheDir() != null) {
-                    // These paths are only available in the browser process.
                     paths[CACHE_DIRECTORY] = appContext.getCacheDir().getPath();
-                    paths[DOWNLOADS_DIRECTORY] = Environment.getExternalStoragePublicDirectory(
-                            Environment.DIRECTORY_DOWNLOADS).getPath();
                 }
                 return paths;
             }
@@ -119,8 +115,8 @@ public static String getThumbnailCacheDirectoryPath(Context appContext) {
     @SuppressWarnings("unused")
     @CalledByNative
     private static String getDownloadsDirectory(Context appContext) {
-        assert sDirPathFetchTask != null : "setDataDirectorySuffix must be called first.";
-        return getDirectoryPath(DOWNLOADS_DIRECTORY);
+        return Environment.getExternalStoragePublicDirectory(
+                Environment.DIRECTORY_DOWNLOADS).getPath();
     }
 
     /**