Use mojo.common.mojom.FilePath to represent file paths

BUG=690020

Review-Url: https://codereview.chromium.org/2842163003
Cr-Commit-Position: refs/heads/master@{#467812}

components/chrome_cleaner/public/interfaces/BUILD.gn

@@ -8,4 +8,7 @@ mojom("interfaces") {
   sources = [
     "chrome_prompt.mojom",
   ]
+  deps = [
+    "//mojo/common:common_custom_types",
+  ]
 }

components/chrome_cleaner/public/interfaces/chrome_prompt.mojom

@@ -4,6 +4,8 @@
 
 module chrome_cleaner.mojom;
 
+import "mojo/common/file_path.mojom";
+
 // The behaviours that have been observed for a given UwS.
 struct ObservedBehaviours {
   bool ad_injector;
@@ -27,7 +29,7 @@ struct UwS {
 
   // List of fully-qualified paths of the files that will be deleted by the
   // Chrome Cleanup Tool for this unwanted software.
-  array<string> files_to_delete;
+  array<mojo.common.mojom.FilePath> files_to_delete;
 };
 
 // Indicates if elevation will be required for cleanup.