buffet: Added advanced error reporting

Created chromeos::Error class that encapsulates rich error
information from various system domains.

Swept GCD device registration, HTTP transport and utilities
to always return additional error information when the caller
requests it. This includes internal errors, general HTTP errors
as well as parsing and returning specific GCD and OAuth2 server
error responses.

Also fixed a number of existing linter warnings.

BUG=chromium:366709
TEST=All existing and new unit tests pass.

Change-Id: Ic01622a8efa3dc365ec106e595b09536818b9b23
Reviewed-on: https://chromium-review.googlesource.com/198772
Tested-by: Alex Vakulenko <avakulenko@chromium.org>
Reviewed-by: Christopher Wiley <wiley@chromium.org>
Commit-Queue: Alex Vakulenko <avakulenko@chromium.org>

buffet/http_connection_curl.h

diff --git a/buffet/http_connection_curl.h b/buffet/http_connection_curl.h
index 0cf34e8..d588854 100644
--- a/buffet/http_connection_curl.h
+++ b/buffet/http_connection_curl.h
@@ -27,9 +27,10 @@
 
   // Overrides from http::Connection.
   // See http_connection.h for description of these methods.
-  virtual bool SendHeaders(const HeaderList& headers) override;
-  virtual bool WriteRequestData(const void* data, size_t size) override;
-  virtual bool FinishRequest() override;
+  virtual bool SendHeaders(const HeaderList& headers, ErrorPtr* error) override;
+  virtual bool WriteRequestData(const void* data, size_t size,
+                                ErrorPtr* error) override;
+  virtual bool FinishRequest(ErrorPtr* error) override;
 
   virtual int GetResponseStatusCode() const override;
   virtual std::string GetResponseStatusText() const override;
@@ -38,8 +39,7 @@
      const std::string& header_name) const override;
   virtual uint64_t GetResponseDataSize() const override;
   virtual bool ReadResponseData(void* data, size_t buffer_size,
-                                size_t* size_read) override;
-  virtual std::string GetErrorMessage() const override;
+                                size_t* size_read, ErrorPtr* error) override;
 
  protected:
   // Write data callback. Used by CURL when receiving response data.
@@ -65,11 +65,9 @@
   // After request has been sent, contains the received response headers.
   std::map<std::string, std::string> headers_;
 
-  // CURL error message in case request fails completely.
-  std::string error_;
   // HTTP protocol version, such as HTTP/1.1
   std::string protocol_version_;
-  // Reponse status text, such as "OK" for 200, or "Forbidden" for 403
+  // Response status text, such as "OK" for 200, or "Forbidden" for 403
   std::string status_text_;
   // Flag used when parsing response headers to separate the response status
   // from the rest of response headers.
@@ -85,4 +83,4 @@
 }  // namespace http
 }  // namespace chromeos
 
-#endif // BUFFET_HTTP_CONNECTION_CURL_H_
+#endif  // BUFFET_HTTP_CONNECTION_CURL_H_