Add utility method for WebString to base::FilePath conversion

content/shell/renderer/layout_test/blink_test_runner.cc

Index: content/shell/renderer/layout_test/blink_test_runner.cc
diff --git a/content/shell/renderer/layout_test/blink_test_runner.cc b/content/shell/renderer/layout_test/blink_test_runner.cc
index 0a2bebaee559eb465a070021987fd8fc8c3f2052..cfcfcf215eb025e6f4a0dbe10fb993b1607d1a82 100644
--- a/content/shell/renderer/layout_test/blink_test_runner.cc
+++ b/content/shell/renderer/layout_test/blink_test_runner.cc
@@ -57,6 +57,7 @@
 #include "net/base/filename_util.h"
 #include "net/base/net_errors.h"
 #include "skia/ext/platform_canvas.h"
+#include "third_party/WebKit/public/platform/FilePathConversion.h"
 #include "third_party/WebKit/public/platform/Platform.h"
 #include "third_party/WebKit/public/platform/WebCString.h"
 #include "third_party/WebKit/public/platform/WebPoint.h"
@@ -327,7 +328,7 @@ WebString BlinkTestRunner::RegisterIsolatedFileSystem(
     const blink::WebVector<blink::WebString>& absolute_filenames) {
   std::vector<base::FilePath> files;
   for (size_t i = 0; i < absolute_filenames.size(); ++i)
-    files.push_back(base::FilePath::FromUTF16Unsafe(absolute_filenames[i]));

[Nico, 2016/02/15 16:45:14]

Before:

On Windows: One conversion from WebString to string16
On Mac, Android, CrOS (SYSTEM_NATIVE_UTF8): one conversion to string16, then one
from utf16 to utf8
On Linux: One conversion from WebString to string16, then another from utf16 to
wstring, and then an elaborate SysWideToNativeMB


The WebString to string16 conversion goes through base::Latin1OrUTF16ToUTF16()
(what a strange function!) which effectively always does a copy

So currently 2 conversions on non-linux, more there

+    files.push_back(blink::WebStringToFilePath(absolute_filenames[i]));
   std::string filesystem_id;
   Send(new LayoutTestHostMsg_RegisterIsolatedFileSystem(
       routing_id(), files, &filesystem_id));