Revert "Don't assume POSIX is UTF8 in FilePathToWebString"

It breaks All/RenderFrameHostManagerTest.DontSelectInvalidFiles.

After re-enabling the
content_browsertests --gtest_also_run_disabled_tests --gtest_filter="All/RenderFrameHostManagerTest.DontSelectInvalidFiles/0" --gtest_repeat=20

passes with this revert.


Bug: 1094938
Change-Id: I965b7d604f8df277e631de938ebebee3ac898023
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2248380
Commit-Queue: Kentaro Hara <haraken@chromium.org>
Auto-Submit: Fergal Daly <fergal@chromium.org>
Reviewed-by: Kentaro Hara <haraken@chromium.org>
Cr-Commit-Position: refs/heads/master@{#779160}

third_party/blink/renderer/platform/exported/file_path_conversion.cc

@@ -40,7 +40,7 @@ WebString FilePathToWebString(const base::FilePath& path) {
     return WebString();
 
 #if defined(OS_POSIX)
-  return WebString::FromUTF8(path.AsUTF8Unsafe());
+  return WebString::FromUTF8(path.value());
 #else
   return WebString::FromUTF16(path.AsUTF16Unsafe());
 #endif