Enable new AltGraph modifier behaviour by default.

Use --disable-features=FixAltGraph to return to the old behaviour.

Bug: 25503
Change-Id: I1297812b5c6201d84b46ae4f4b320ed5e403f7a1
Reviewed-on: https://chromium-review.googlesource.com/963790Reviewed-by: Rick Byers <rbyers@chromium.org>
Commit-Queue: Wez <wez@chromium.org>
Cr-Commit-Position: refs/heads/master@{#543383}

ui/events/keycodes/platform_key_map_win.cc

@@ -279,7 +279,7 @@ base::LazyInstance<base::ThreadLocalStorage::Slot,
 
 // TODO(crbug.com/25503): Controls Control+Alt vs AltGraph disambiguation.
 const base::Feature kFixAltGraphModifier{"FixAltGraph",
-                                         base::FEATURE_DISABLED_BY_DEFAULT};
+                                         base::FEATURE_ENABLED_BY_DEFAULT};
 
 }  // anonymous namespace