[fsp] Fix crash because of calling net::GetMimeTypeFromFile on UI thread.

chrome/browser/extensions/api/file_handlers/mime_util.cc

Index: chrome/browser/extensions/api/file_handlers/mime_util.cc
diff --git a/chrome/browser/extensions/api/file_handlers/mime_util.cc b/chrome/browser/extensions/api/file_handlers/mime_util.cc
index 47400563224d3af66749806d5b64343e1a78ff4b..28c6f93f80edb2f25f7ecac0c386dfd4abb82c5c 100644
--- a/chrome/browser/extensions/api/file_handlers/mime_util.cc
+++ b/chrome/browser/extensions/api/file_handlers/mime_util.cc
@@ -41,10 +41,18 @@ void SniffMimeType(const base::FilePath& local_path, std::string* result) {
 }
 
 #if defined(OS_CHROMEOS)
+// Converts a result passed as a scoped pointer to a dereferenced value passed
+// to |callback|.
+void OnGetMimeTypeFromFileForNonNativeLocalPathCompleted(
+    scoped_ptr<std::string> mime_type,
+    const base::Callback<void(const std::string&)>& callback) {
+  callback.Run(*mime_type);
+}
+
 // Called when fetching MIME type for a non-native local path is completed.
 // If |success| is false, then tries to guess the MIME type by looking at the
 // file name.
-void OnGetMimeTypeForNonNativeLocalPathCompleted(
+void OnGetMimeTypeFromMetadataForNonNativeLocalPathCompleted(
     const base::FilePath& local_path,
     const base::Callback<void(const std::string&)>& callback,
     bool success,
@@ -54,9 +62,19 @@ void OnGetMimeTypeForNonNativeLocalPathCompleted(
     return;
   }
 
-  std::string mime_type_from_extension;
-  net::GetMimeTypeFromFile(local_path, &mime_type_from_extension);
-  callback.Run(mime_type_from_extension);
+  // MIME type not available with metadata, hence try to guess is from the

[not at google - send to devlin, 2014/07/08 16:02:28]

s/is/it

[mtomasz, 2014/07/09 02:21:02]

Done.

+  // file's extension.
+  scoped_ptr<std::string> mime_type_from_extension(new std::string);
+  std::string* const mime_type_from_extension_ptr =
+      mime_type_from_extension.get();

[not at google - send to devlin, 2014/07/08 16:02:28]

this pattern is such a pain :( it seems like it's not a great fit for
PostBlockingPoolTaskAndReply. would it be easier to just use
PostBlockingPoolTask and manage the fetch/reply yourself?

i.e. basically a much simple async-ifying of all of this logic?

i.e. make GetMimeTypeForLocalPath post to the blocking pool with a method like
GetMimeTypeForLocalPathOnBlockingPool which is basically
GetMimeTypeForLocalPath?

[mtomasz, 2014/07/09 02:21:02]

I'm not a huge fan of it either, but this pattern is often used for
Post*TaskAndReply() in Chromium code and I've been asked several times by
reviewers to go this way rather than post the answer back manually.

WDYT?

[not at google - send to devlin, 2014/07/09 02:38:20]

alright.

but let it be on the record that I think ^ is a much simpler transformation.

+  BrowserThread::PostBlockingPoolTaskAndReply(
+      FROM_HERE,
+      base::Bind(base::IgnoreResult(&net::GetMimeTypeFromFile),
+                 local_path,
+                 mime_type_from_extension_ptr),
+      base::Bind(&OnGetMimeTypeFromFileForNonNativeLocalPathCompleted,
+                 base::Passed(&mime_type_from_extension),
+                 callback));
 }
 #endif
 
@@ -69,6 +87,29 @@ void OnSniffMimeTypeForNativeLocalPathCompleted(
 
 }  // namespace
 
+// Handles response of net::GetMimeTypeFromFile for native file systems. If
+// MIME type is available, then forwards it to |callback|. Otherwise, fallbacks
+// to sniffing.
+void OnGetMimeTypeFromFileForNativeLocalPathCompleted(
+    const base::FilePath& local_path,
+    scoped_ptr<std::string> mime_type,
+    const base::Callback<void(const std::string&)>& callback) {
+  if (!mime_type->empty()) {
+    callback.Run(*mime_type);
+    return;
+  }
+
+  scoped_ptr<std::string> sniffed_mime_type(new std::string);
+  std::string* const sniffed_mime_type_ptr = sniffed_mime_type.get();
+  BrowserThread::PostBlockingPoolTaskAndReply(
+      FROM_HERE,
+      base::Bind(&SniffMimeType, local_path, sniffed_mime_type_ptr),
+      base::Bind(&OnSniffMimeTypeForNativeLocalPathCompleted,
+                 base::Passed(&sniffed_mime_type),
+                 callback));
+}
+
+// Fetches MIME type for a local path and returns it with a |callback|.
 void GetMimeTypeForLocalPath(
     Profile* profile,
     const base::FilePath& local_path,
@@ -81,7 +122,7 @@ void GetMimeTypeForLocalPath(
     file_manager::util::GetNonNativeLocalPathMimeType(
         profile,
         local_path,
-        base::Bind(&OnGetMimeTypeForNonNativeLocalPathCompleted,
+        base::Bind(&OnGetMimeTypeFromMetadataForNonNativeLocalPathCompleted,
                    local_path,
                    callback));
     return;
@@ -89,20 +130,19 @@ void GetMimeTypeForLocalPath(
 #endif
 
   // For native local files, try to guess the mime from the extension. If
-  // not availble, then try to sniff if.
-  std::string mime_type_from_extension;
-  if (net::GetMimeTypeFromFile(local_path, &mime_type_from_extension)) {
-    callback.Run(mime_type_from_extension);
-  } else {
-    scoped_ptr<std::string> sniffed_mime_type(new std::string);
-    std::string* sniffed_mime_type_ptr = sniffed_mime_type.get();
-    BrowserThread::PostBlockingPoolTaskAndReply(
-        FROM_HERE,
-        base::Bind(&SniffMimeType, local_path, sniffed_mime_type_ptr),
-        base::Bind(&OnSniffMimeTypeForNativeLocalPathCompleted,
-                   base::Passed(&sniffed_mime_type),
-                   callback));
-  }
+  // not available, then try to sniff if.
+  scoped_ptr<std::string> mime_type_from_extension(new std::string);
+  std::string* const mime_type_from_extension_ptr =
+      mime_type_from_extension.get();
+  BrowserThread::PostBlockingPoolTaskAndReply(
+      FROM_HERE,
+      base::Bind(base::IgnoreResult(&net::GetMimeTypeFromFile),
+                 local_path,
+                 mime_type_from_extension_ptr),
+      base::Bind(&OnGetMimeTypeFromFileForNativeLocalPathCompleted,
+                 local_path,
+                 base::Passed(&mime_type_from_extension),
+                 callback));
 }
 
 MimeTypeCollector::MimeTypeCollector(Profile* profile)