Provide JS tests absolute file path

Case:
1. Start any js browser_test
2. Open dev tools
3. All test js files will be listed all together without any host or
   folders

It's not very convenient behavior for debugging tests. For example it's
very difficult to map them to local files with vscode or webstorm.

Suggestion is to add absolute path to test files. This will group them
in dev tools in correct tree and automaticly map in external debugger.

Change-Id: If30c27e395c9cfc100469b740936c0f4e615b0ba
Reviewed-on: https://chromium-review.googlesource.com/947944Reviewed-by: Scott Violet <sky@chromium.org>
Reviewed-by: David Tseng <dtseng@chromium.org>
Commit-Queue: Scott Violet <sky@chromium.org>
Cr-Commit-Position: refs/heads/master@{#543126}

chrome/test/base/OWNERS

 per-file js2gtest.*=dtseng@chromium.org
+per-file javascript_browser_test.*=dtseng@chromium.org
 
 per-file *tracing*=file://base/trace_event/OWNERS
 

chrome/test/base/javascript_browser_test.cc

@@ -11,6 +11,7 @@
 #include "chrome/common/chrome_paths.h"
 #include "components/nacl/common/buildflags.h"
 #include "content/public/browser/web_ui.h"
+#include "net/base/filename_util.h"
 #include "ui/base/resource/resource_bundle.h"
 
 // static
@@ -85,9 +86,11 @@ void JavaScriptBrowserTest::BuildJavascriptLibraries(
        user_libraries_iterator != user_libraries_.end();
        ++user_libraries_iterator) {
     std::string library_content;
+    base::FilePath library_absolute_path;
     if (user_libraries_iterator->IsAbsolute()) {
+      library_absolute_path = *user_libraries_iterator;
       ASSERT_TRUE(
-          base::ReadFileToString(*user_libraries_iterator, &library_content))
+          base::ReadFileToString(library_absolute_path, &library_content))
           << user_libraries_iterator->value();
     } else {
       bool ok = false;
@@ -95,10 +98,9 @@ void JavaScriptBrowserTest::BuildJavascriptLibraries(
       for (library_search_path_iterator = library_search_paths_.begin();
            library_search_path_iterator != library_search_paths_.end();
            ++library_search_path_iterator) {
-        ok = base::ReadFileToString(
-            base::MakeAbsoluteFilePath(
-                library_search_path_iterator->Append(*user_libraries_iterator)),
-            &library_content);
+        library_absolute_path = base::MakeAbsoluteFilePath(
+            library_search_path_iterator->Append(*user_libraries_iterator));
+        ok = base::ReadFileToString(library_absolute_path, &library_content);
         if (ok)
           break;
       }
@@ -109,7 +111,8 @@ void JavaScriptBrowserTest::BuildJavascriptLibraries(
 
     // This magic code puts filenames in stack traces.
     library_content.append("//# sourceURL=");
-    library_content.append(user_libraries_iterator->BaseName().AsUTF8Unsafe());
+    library_content.append(
+        net::FilePathToFileURL(library_absolute_path).spec());
     library_content.append("\n");
     libraries->push_back(base::UTF8ToUTF16(library_content));
   }