Specify output files of do_generate_fontconfig_caches explicitly

This does not allow arbitrary files are included in isolated input from fontconfig_caches directory.

Bug: 870622
Change-Id: I69bc8993800f263d7e3d7679ed85f9c79a380a0b
Reviewed-on: https://chromium-review.googlesource.com/1163596Reviewed-by: Thomas Anderson <thomasanderson@chromium.org>
Reviewed-by: Erik Chen <erikchen@chromium.org>
Reviewed-by: Nico Weber <thakis@chromium.org>
Commit-Queue: Takuto Ikuta <tikuta@chromium.org>
Cr-Commit-Position: refs/heads/master@{#581056}

base/test/BUILD.gn

@@ -378,7 +378,7 @@ if (is_linux) {
       ]
       args = []
       outputs = [
-        "$root_out_dir/fontconfig_caches/",
+        "$root_out_dir/fontconfig_caches/df1acc8c-39d5-4a8b-8507-b1a7396ac3ac-le64.cache-7",
         "$root_out_dir/test_fonts/.uuid",
       ]
     }

base/test/generate_fontconfig_caches.cc

@@ -12,6 +12,7 @@
 #include "base/files/file_path.h"
 #include "base/files/file_util.h"
 #include "base/path_service.h"
+#include "base/strings/strcat.h"
 #include "base/test/fontconfig_util_linux.h"
 
 // GIANT WARNING: The point of this file is to front-load construction of the
@@ -21,7 +22,7 @@
 // deterministic. This executable tries to set some external state to ensure
 // determinism. We have no way of guaranteeing that this produces correct
 // results, or even has the intended effect.
-int main(void) {
+int main() {
   // fontconfig generates a random uuid and uses it to match font folders with
   // the font cache. Rather than letting fontconfig generate a random uuid,
   // which introduces build non-determinism, we place a fixed uuid in the font
@@ -46,13 +47,17 @@ int main(void) {
   new_times.modtime = 123456789;
   utime(test_fonts_file_path.value().c_str(), &new_times);
 
+  base::FilePath fontconfig_caches = dir_module.Append("fontconfig_caches");
+
+  // Delete directory before generating fontconfig caches. This will notify
+  // future fontconfig_caches changes.
+  CHECK(base::DeleteFile(fontconfig_caches, /*recursive=*/true));
+
   base::SetUpFontconfig();
   base::TearDownFontconfig();
 
-  base::FilePath fontconfig_caches = dir_module.Append("fontconfig_caches");
-  CHECK(base::DirectoryExists(fontconfig_caches));
-  base::FilePath stamp = fontconfig_caches.Append("STAMP");
-  CHECK_EQ(0, base::WriteFile(stamp, "", 0));
-
+  // Check existence of intended fontconfig cache file.
+  CHECK(base::PathExists(
+      fontconfig_caches.Append(base::StrCat({uuid, "-le64.cache-7"}))));
   return 0;
 }

third_party/test_fonts/README.chromium

@@ -27,7 +27,9 @@ How to update or add fonts:
 6.  Add all the font_bundle.tar.gz.sha1 file to the chromium src repository, by
     executing the following command:
 	$ git add ./third_party/test_fonts/test_fonts.tar.gz.sha1
-7.  (optional) Update FONT_FILES in
+7.  Update filename constant for fontconfig cache in //base/test/BUILD.gn and
+    //base/test/generate_fontconfig_caches.cc when test fonts change.
+8.  (optional) Update FONT_FILES in
     third_party/blink/tools/blinkpy/web_tests/port/base.py .
 
 If you need access to the chromium-fonts bucket, contact Chrome infra.% For