Separate mutators for text and selection

Previously, TextInputModel's SetEditingState method was a 1:1 mapping of
the underlying protocol used on the text input channel between the
framework and the engine. This breaks it up into two methods, which
allows the selection to be updated independently of the text, and avoids
tying the API the the underlying protocol.

This will becomre more important when we add additional state to support
composing regions for multi-step input methods such as those used for
Japanese.

Author: cbracken

shell/platform/common/cpp/text_input_model.cc

@@ -35,17 +35,20 @@ TextInputModel::TextInputModel()
 
 TextInputModel::~TextInputModel() = default;
 
-bool TextInputModel::SetEditingState(size_t selection_base,
-                                     size_t selection_extent,
-                                     const std::string& text) {
-  if (selection_base > text.size() || selection_extent > text.size()) {
-    return false;
-  }
+void TextInputModel::SetText(const std::string& text) {
   std::wstring_convert<std::codecvt_utf8_utf16<char16_t>, char16_t>
       utf16_converter;
   text_ = utf16_converter.from_bytes(text);
-  selection_base_ = text_.begin() + selection_base;
-  selection_extent_ = text_.begin() + selection_extent;
+  selection_base_ = text_.begin();
+  selection_extent_ = selection_base_;
+}
+
+bool TextInputModel::SetSelection(size_t base, size_t extent) {
+  if (base > text_.size() || extent > text_.size()) {
+    return false;
+  }
+  selection_base_ = text_.begin() + base;
+  selection_extent_ = text_.begin() + extent;
   return true;
 }
 

shell/platform/common/cpp/text_input_model.h

@@ -17,13 +17,15 @@ class TextInputModel {
   TextInputModel();
   virtual ~TextInputModel();
 
-  // Attempts to set the text state.
+  // Sets the text.
   //
-  // Returns false if the state is not valid (base or extent are out of
-  // bounds, or base is less than extent).
-  bool SetEditingState(size_t selection_base,
-                       size_t selection_extent,
-                       const std::string& text);
+  // Resets the selection base and extent.
+  void SetText(const std::string& text);
+
+  // Attempts to set the text selection.
+  //
+  // Returns false if the base or extent are out of bounds.
+  bool SetSelection(size_t base, size_t extent);
 
   // Adds a Unicode code point.
   //