Implement direct write fallback proxy

content/common/dwrite_text_analysis_source_win.h

+// Copyright (c) 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef CONTENT_COMMON_DWRITE_TEXT_ANALYSIS_SOURCE_WIN_H_
+#define CONTENT_COMMON_DWRITE_TEXT_ANALYSIS_SOURCE_WIN_H_
+
+#include <dwrite.h>
+#include <wrl.h>
+
+#include "base/macros.h"
+#include "base/strings/string16.h"
+#include "content/common/content_export.h"
+
+namespace content {
+
+// Implements an IDWriteTextAnalysisSource, describing a single block of text.
+class CONTENT_EXPORT TextAnalysisSource

[ananta, 2016/04/12 23:44:39]

Please add some comments about when this class is used, etc.

[Ilya Kulshin, 2016/04/13 01:33:29]

This class doesn't really have any special use aside from being useful when
someone needs a really basic implementation of IDWriteTextAnalysisSource. Can
you explain what information you would like to see in a comment?

[ananta, 2016/04/13 23:31:09]

If we have a use case in the current patch, pointing to that would be helpful
for reference.

[Ilya Kulshin, 2016/04/13 23:59:40]

Such a comment would certainly become outdated, and would be hard to notice that
it needs to be updated at that time. Since TextAnalysisSource is not a common
token, actual users can be easily found with codesearch.

On the question of being used specifically in this patch, it is used by
DWriteFontProxyMessageFilter::OnMapCharacters and
FontFallbackUnitTest::MapCharacters.

+    : public Microsoft::WRL::RuntimeClass<
+          Microsoft::WRL::RuntimeClassFlags<Microsoft::WRL::ClassicCom>,
+          IDWriteTextAnalysisSource> {
+ public:
+  HRESULT STDMETHODCALLTYPE GetLocaleName(UINT32 text_position,
+                                          UINT32* text_length,
+                                          const WCHAR** locale_name) override;
+  HRESULT STDMETHODCALLTYPE GetNumberSubstitution(

[ananta, 2016/04/12 23:44:39]

newline between methods.

[Ilya Kulshin, 2016/04/13 01:33:29]

Added a comment to make it clear that these are overrides of the
IDWriteTextAnalysisSource interface, which don't require a newline (it's clearer
which methods are part of the interface when there are no linebreaks).

+      UINT32 text_position,
+      UINT32* text_length,
+      IDWriteNumberSubstitution** number_substitution) override;
+  DWRITE_READING_DIRECTION STDMETHODCALLTYPE
+  GetParagraphReadingDirection() override;
+  HRESULT STDMETHODCALLTYPE GetTextAtPosition(UINT32 text_position,
+                                              const WCHAR** text_string,
+                                              UINT32* text_length) override;
+  HRESULT STDMETHODCALLTYPE GetTextBeforePosition(UINT32 text_position,
+                                                  const WCHAR** text_string,
+                                                  UINT32* text_length) override;
+
+  HRESULT STDMETHODCALLTYPE
+  RuntimeClassInitialize(const base::string16& text,
+                         const base::string16& locale_name,
+                         IDWriteNumberSubstitution* number_substitution,
+                         DWRITE_READING_DIRECTION reading_direction);
+
+ protected:
+  ~TextAnalysisSource();
+
+ private:
+  base::string16 text_;
+  base::string16 locale_name_;
+  Microsoft::WRL::ComPtr<IDWriteNumberSubstitution> number_substitution_;

[ananta, 2016/04/12 23:44:39]

Some comments about the non obvious members would be nice.

[Ilya Kulshin, 2016/04/13 01:33:29]

Added some explanatory comments in the header. The members just hold data that
is returned as-is on demand. Can you suggest what additional explanatory
comments you think are necessary?

+  DWRITE_READING_DIRECTION reading_direction_;
+
+  DISALLOW_ASSIGN(TextAnalysisSource);
+};
+
+}  // namespace content
+
+#endif  // CONTENT_COMMON_DWRITE_TEXT_ANALYSIS_SOURCE_WIN_H_