ozone/wayland: Handle preedit string in WaylandInputMethodContext

As of [1], UTF characteres are correctly composed on Ozone/wayland,
taking as input raw key events from InputMethod classes. That is
possible thanks to previously ChromeOS-only CharacterComposer component.
This patch fixes the preedit text handling in WaylandInputMethodContext,
which basically properly support HEX_MODE in CharacterComposer.

[1] https://chromium-review.googlesource.com/c/chromium/src/+/1448136

R=rjkroege@chromium.org, shuchen@chromium.org

Bug: 921947
Change-Id: I7cf750df2bf43273464f52a726719d50d74075f8
Reviewed-on: https://chromium-review.googlesource.com/c/1454297Reviewed-by: Michael Spang <spang@chromium.org>
Reviewed-by: Robert Kroeger <rjkroege@chromium.org>
Reviewed-by: Shu Chen <shuchen@chromium.org>
Commit-Queue: Nick Yamane <nickdiego@igalia.com>
Cr-Commit-Position: refs/heads/master@{#630679}

ui/ozone/platform/wayland/DEPS

@@ -4,6 +4,7 @@ include_rules = [
   "+ui/base/ui_base_features.h",
   "+ui/base/ime/character_composer.h",
   "+ui/base/ime/composition_text.h",
+  "+ui/base/ime/ime_text_span.h",
   "+ui/base/ime/linux/linux_input_method_context.h",
   "+ui/base/ime/linux/linux_input_method_context_factory.h",
   "+mojo/public",

ui/ozone/platform/wayland/wayland_input_method_context.cc

@@ -10,6 +10,7 @@
 #include "base/strings/string_util.h"
 #include "base/strings/utf_string_conversions.h"
 #include "ui/base/ime/composition_text.h"
+#include "ui/base/ime/ime_text_span.h"
 #include "ui/events/base_event_utils.h"
 #include "ui/events/event.h"
 #include "ui/events/keycodes/dom/dom_code.h"
@@ -74,13 +75,27 @@ bool WaylandInputMethodContext::DispatchKeyEvent(
       !character_composer_.FilterKeyPress(key_event))
     return false;
 
-  // TODO(nickdiego): Handle preedit string
+  // CharacterComposer consumed the key event. Update the composition text.
+  UpdatePreeditText(character_composer_.preedit_string());
   auto composed = character_composer_.composed_character();
   if (!composed.empty())
     delegate_->OnCommit(composed);
   return true;
 }
 
+void WaylandInputMethodContext::UpdatePreeditText(
+    const base::string16& preedit_text) {
+  CompositionText preedit;
+  preedit.text = preedit_text;
+  auto length = preedit.text.size();
+
+  preedit.selection = gfx::Range(length);
+  preedit.ime_text_spans.push_back(
+      ImeTextSpan(ImeTextSpan::Type::kComposition, 0, length,
+                  ImeTextSpan::Thickness::kThin, SK_ColorTRANSPARENT));
+  delegate_->OnPreeditChanged(preedit);
+}
+
 void WaylandInputMethodContext::Reset() {
   character_composer_.Reset();
   if (text_input_)

ui/ozone/platform/wayland/wayland_input_method_context.h

@@ -5,6 +5,9 @@
 #ifndef UI_OZONE_PLATFORM_WAYLAND_WAYLAND_INPUT_METHOD_CONTEXT_H_
 #define UI_OZONE_PLATFORM_WAYLAND_WAYLAND_INPUT_METHOD_CONTEXT_H_
 
+#include <memory>
+#include <string>
+
 #include "base/macros.h"
 #include "ui/base/ime/character_composer.h"
 #include "ui/base/ime/linux/linux_input_method_context.h"
@@ -43,6 +46,8 @@ class WaylandInputMethodContext : public LinuxInputMethodContext,
   void OnKeysym(uint32_t key, uint32_t state, uint32_t modifiers) override;
 
  private:
+  void UpdatePreeditText(const base::string16& preedit_text);
+
   WaylandConnection* connection_ = nullptr;  // TODO(jani) Handle this better
 
   // Delegate interface back to IME code in ui.