Add support for animations in vector icons.

ui/gfx/vector_icon_types.h

Index: ui/gfx/vector_icon_types.h
diff --git a/ui/gfx/vector_icon_types.h b/ui/gfx/vector_icon_types.h
index b18000b41fe304b8ade4ae9bdde408243741b068..27d21c3bbc6ee3270e9dbfeb0a924c48c537c4e8 100644
--- a/ui/gfx/vector_icon_types.h
+++ b/ui/gfx/vector_icon_types.h
@@ -58,6 +58,11 @@ enum CommandType {
   // Flips the x-axis in RTL locales. Default is false, this command sets it to
   // true.
   FLIPS_IN_RTL,
+  // Defines a timed transition for other elements.
+  TRANSITION_FROM,
+  TRANSITION_TO,
+  // Parameters are delay (ms), duration (ms), and tween type.

[sadrul, 2017/05/11 04:22:55]

Please also include how the tween type is defined (e.g. string? some int value
corresponding to some enum?)

[Evan Stade, 2017/05/11 16:16:26]

Done, but it seems that will be apparent once animated icons exist in the
codebase (git grep TRANSITION_END will immediately drum up some examples to work
from, e.g.

  TRANSITION_END, 100, 250, gfx::Tween::FAST_OUT_SLOW_IN,

+  TRANSITION_END,
   // Marks the end of the list of commands.
   END
 };