Add GL_EXT_color_buffer_half_float support

cc/resources/resource_provider.cc

Index: cc/resources/resource_provider.cc
diff --git a/cc/resources/resource_provider.cc b/cc/resources/resource_provider.cc
index 83aaa006266702f5e699163630bb9fedc696b34a..dd900f84d5c07015a5b2005a390d1ae2434b73ae 100644
--- a/cc/resources/resource_provider.cc
+++ b/cc/resources/resource_provider.cc
@@ -547,7 +547,8 @@ bool ResourceProvider::IsResourceFormatSupported(ResourceFormat format) const {
       // TODO(ccameron): This will always return false on pixel tests, which
       // makes it un-test-able until we upgrade Mesa.
       // https://crbug.com/687720
-      return caps.texture_half_float_linear && caps.color_buffer_float;
+      return caps.texture_half_float_linear &&
+             caps.color_buffer_half_float_rgba;
   }
 
   NOTREACHED();