Symlink default rr trace directory in dummy home directory.

rr defaults to writing the trace to $HOME/.local/share/rr but run-webkit-tests
creates a dummy home directory that is deleted after tests run. In order to
make this "just work" we can symlink .local/share/rr to the real directory if
it exists.

Bug: 817861
Change-Id: I845c023c3be98835bddb757dad9a18231c7e69ce
Reviewed-on: https://chromium-review.googlesource.com/943826Reviewed-by: Dirk Pranke <dpranke@chromium.org>
Commit-Queue: Robert Flack <flackr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#540281}

third_party/WebKit/Tools/Scripts/webkitpy/layout_tests/port/linux.py

@@ -141,12 +141,14 @@ class LinuxPort(base.Port):
             if not fs.exists(original_path):
                 continue
             fs.copyfile(original_path, fs.join(dummy_home, filename))
-        # Prevent fontconfig etc. from reconstructing the cache.
-        for dirname in ['.cache']:
-            original_path = fs.join(self._original_home, dirname)
+        # Prevent fontconfig etc. from reconstructing the cache and symlink rr
+        # trace directory.
+        for dirpath in [['.cache'], ['.local', 'share', 'rr']]:
+            original_path = fs.join(self._original_home, *dirpath)
             if not fs.exists(original_path):
                 continue
-            fs.symlink(original_path, fs.join(dummy_home, dirname))
+            fs.maybe_make_directory(fs.join(dummy_home, *dirpath[:-1]))
+            fs.symlink(original_path, fs.join(dummy_home, *dirpath))
 
     def _clean_up_dummy_home_dir(self):
         """Cleans up the dummy dir and resets the HOME environment variable."""