Supports the invisible underline for native input fields.

ui/base/ime/composition_text.cc

Index: ui/base/ime/composition_text.cc
diff --git a/ui/base/ime/composition_text.cc b/ui/base/ime/composition_text.cc
index f85bc7487587d7aa85d3c104faec92e302e82064..325294174c9c5ac0de029dde9d2510dafcde20c1 100644
--- a/ui/base/ime/composition_text.cc
+++ b/ui/base/ime/composition_text.cc
@@ -7,6 +7,8 @@
 namespace ui {
 
 CompositionText::CompositionText() {
+  underlines.push_back(CompositionUnderline());

[msw, 2015/03/26 20:22:48]

Why do we need this change? It seems odd to add this underline to an empty
CompositionText object if it's just needed to accomodate
TextfieldModel::SetCompositionText's behavior at line 570: "if
(composition.underlines.size() > 0 && composition.underlines[0].color != 0)".

If we just want the textfield's composition range to be underlined by default,
unless the underline is specifically set to transparent, perhaps change the
condition in TextfieldModel::SetCompositionText to "if
(composition.underlines.empty() || composition.underlines[0].color != 0)"

[Shu Chen, 2015/03/30 03:56:21]

It was to make the tests can pass.
I've just checked the latest patchset that the test can still pass without this
hack.
So I just reverted this change. Thanks for catching!

+  underlines[0].color = SK_ColorBLACK;
 }
 
 CompositionText::~CompositionText() {