Extension content verifier: ignore empty relative paths

Some extensions make a request to "/" which confuses the extension
content verifier and causes it to mark the extension as corrupted.

Bug: 791929
Change-Id: Id594bd714048d33ddcf88fa86b26ce0a7696503c
Reviewed-on: https://chromium-review.googlesource.com/809225
Commit-Queue: proberge <proberge@chromium.org>
Reviewed-by: Devlin <rdevlin.cronin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#521777}

extensions/browser/content_hash_reader.cc

@@ -79,7 +79,11 @@ bool ContentHashReader::Init() {
   if (!verified_contents.HasTreeHashRoot(relative_path_)) {
     // Making a request to a non-existent resource should not result in
     // content verification failure.
-    if (!base::PathExists(extension_root_.Append(relative_path_)))
+    // TODO(proberge): The relative_path_.empty() check should be moved higher
+    // in the execution flow for performance wins by saving on costly IO
+    // operations and calculations.
+    if (relative_path_.empty() ||
+        !base::PathExists(extension_root_.Append(relative_path_)))
       file_missing_from_verified_contents_ = true;
 
     return false;

extensions/browser/content_verify_job_unittest.cc

@@ -207,6 +207,17 @@ TEST_F(ContentVerifyJobUnittest, DeletedAndMissingFiles) {
               RunContentVerifyJob(*extension.get(), unexpected_resource_path,
                                   contents));
   }
+
+  {
+    // Ask for the root path of the extension (i.e., chrome-extension://<id>/).
+    // Verification should skip this request as if the resource were
+    // non-existent. See https://crbug.com/791929.
+    base::FilePath empty_path_resource_path(FILE_PATH_LITERAL(""));
+    std::string empty_contents;
+    EXPECT_EQ(ContentVerifyJob::NONE,
+              RunContentVerifyJob(*extension.get(), empty_path_resource_path,
+                                  empty_contents));
+  }
 }
 
 // Tests that content modification causes content verification failure.