[gpu] Switch to std::tuple for FormatType.

Now that std::tuple is allowed, there is no need to construct a
struct for FormatType.

Bug: None
Cq-Include-Trybots: master.tryserver.chromium.android:android_optional_gpu_tests_rel;master.tryserver.chromium.linux:linux_optional_gpu_tests_rel;master.tryserver.chromium.mac:mac_optional_gpu_tests_rel;master.tryserver.chromium.win:win_optional_gpu_tests_rel
Change-Id: I8294ff9d3a1e78ca59da95ae9d7c69b9635c0afb
Reviewed-on: https://chromium-review.googlesource.com/832367
Commit-Queue: Rijubrata Bhaumik <rijubrata.bhaumik@intel.com>
Reviewed-by: Zhenyao Mo <zmo@chromium.org>
Cr-Commit-Position: refs/heads/master@{#524980}
diff --git a/gpu/command_buffer/service/texture_manager.cc b/gpu/command_buffer/service/texture_manager.cc
index 437e0b9..8a2c00c 100644
--- a/gpu/command_buffer/service/texture_manager.cc
+++ b/gpu/command_buffer/service/texture_manager.cc
@@ -9,6 +9,7 @@
 
 #include <algorithm>
 #include <set>
+#include <tuple>
 #include <utility>
 
 #include "base/bits.h"
@@ -283,21 +284,16 @@
   }
 
  private:
-  // TODO(zmo): once std::tuple is allowed, switch over to that.
-  struct FormatType {
-    GLenum internal_format;
-    GLenum format;
-    GLenum type;
-  };
-
+  // FormatType is a tuple of <internal_format, format, type>
+  typedef std::tuple<GLenum, GLenum, GLenum> FormatType;
   struct FormatTypeCompare {
     bool operator() (const FormatType& lhs, const FormatType& rhs) const {
-      return (lhs.internal_format < rhs.internal_format ||
-              ((lhs.internal_format == rhs.internal_format) &&
-               (lhs.format < rhs.format)) ||
-              ((lhs.internal_format == rhs.internal_format) &&
-               (lhs.format == rhs.format) &&
-               (lhs.type < rhs.type)));
+      return (std::get<0>(lhs) < std::get<0>(rhs) ||
+              ((std::get<0>(lhs) == std::get<0>(rhs)) &&
+               (std::get<1>(lhs) < std::get<1>(rhs))) ||
+              ((std::get<0>(lhs) == std::get<0>(rhs)) &&
+               (std::get<1>(lhs) == std::get<1>(rhs)) &&
+               (std::get<2>(lhs) < std::get<2>(rhs))));
     }
   };