[ozone/x11] Made the platform returning if transparent color would work.

The Textfield::WriteDragDataForView sets transparent background color
for the drag image, which is not always supported on X11 (depends on
whether the compositing manager is available), but Ozone/X11 didn't
check that and always used the transparent color.

This CL adds a new method in the Ozone platform that returns whether
transparent color could be used.

Bug: 1085700
Change-Id: I2c812086993fc825bb8f7bc0d416b7aa4ab44d89
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2323293Reviewed-by: Scott Violet <sky@chromium.org>
Reviewed-by: Maksim Sisov (GMT+3) <msisov@igalia.com>
Commit-Queue: Alexander Dunaev <adunaev@igalia.com>
Cr-Commit-Position: refs/heads/master@{#796738}

ui/base/x/x11_gl_egl_utility.cc

@@ -46,4 +46,8 @@ void ChoosePlatformCustomAlphaAndBufferSize(EGLint* alpha_size,
   }
 }
 
+bool IsTransparentBackgroundSupported() {
+  return ui::XVisualManager::GetInstance()->ArgbVisualAvailable();
+}
+
 }  // namespace ui

ui/base/x/x11_gl_egl_utility.h

@@ -19,6 +19,9 @@ void GetPlatformExtraDisplayAttribs(EGLenum platform_type,
 void ChoosePlatformCustomAlphaAndBufferSize(EGLint* alpha_size,
                                             EGLint* buffer_size);
 
+// Returns whether transparent background is suppored.
+bool IsTransparentBackgroundSupported();
+
 }  // namespace ui
 
-#endif  // UI_BASE_X_X11_GL_EGL_UTILITY_H_
+#endif  // UI_BASE_X_X11_GL_EGL_UTILITY_H_
\ No newline at end of file

ui/ozone/platform/x11/gl_egl_utility_x11.cc

@@ -22,4 +22,8 @@ void GLEGLUtilityX11::ChooseEGLAlphaAndBufferSize(EGLint* alpha_size,
   ChoosePlatformCustomAlphaAndBufferSize(alpha_size, buffer_size);
 }
 
+bool GLEGLUtilityX11::IsTransparentBackgroundSupported() const {
+  return ui::IsTransparentBackgroundSupported();
+}
+
 }  // namespace ui

ui/ozone/platform/x11/gl_egl_utility_x11.h

@@ -23,6 +23,7 @@ class GLEGLUtilityX11 : public PlatformGLEGLUtility {
       std::vector<EGLAttrib>* display_attributes) override;
   void ChooseEGLAlphaAndBufferSize(EGLint* alpha_size,
                                    EGLint* buffer_size) override;
+  bool IsTransparentBackgroundSupported() const override;
 };
 
 }  // namespace ui

ui/ozone/public/platform_gl_egl_utility.h

@@ -27,6 +27,10 @@ class COMPONENT_EXPORT(OZONE_BASE) PlatformGLEGLUtility {
   // Chooses alpha and buffer size values.
   virtual void ChooseEGLAlphaAndBufferSize(EGLint* alpha_size,
                                            EGLint* buffer_size) = 0;
+
+  // Returns whether the platform supports setting transparent background for
+  // windows.
+  virtual bool IsTransparentBackgroundSupported() const = 0;
 };
 
 }  // namespace ui

ui/views/controls/textfield/textfield.cc

@@ -71,7 +71,6 @@
 #endif
 
 #if defined(USE_X11)
-#include "ui/base/ui_base_features.h"
 #include "ui/base/x/x11_util.h"  // nogncheck
 #endif
 
@@ -85,6 +84,12 @@
 #include "ui/base/cocoa/secure_password_input.h"
 #endif
 
+#if defined(USE_OZONE)
+#include "ui/base/ui_base_features.h"
+#include "ui/ozone/public/ozone_platform.h"
+#include "ui/ozone/public/platform_gl_egl_utility.h"
+#endif
+
 namespace views {
 
 namespace {
@@ -274,6 +279,24 @@ bool IsValidCharToInsert(const base::char16& ch) {
   return (ch >= 0x20 && ch < 0x7F) || ch > 0x9F;
 }
 
+bool CanUseTransparentBackgroundForDragImage() {
+#if defined(USE_OZONE)
+  if (::features::IsUsingOzonePlatform()) {
+    const auto* const egl_utility =
+        ui::OzonePlatform::GetInstance()->GetPlatformGLEGLUtility();
+    return egl_utility ? egl_utility->IsTransparentBackgroundSupported()
+                       : false;
+  }
+#endif
+#if defined(USE_X11)
+  // Fallback on the background color if the system doesn't support compositing.
+  return ui::XVisualManager::GetInstance()->ArgbVisualAvailable();
+#else
+  // Other platforms allow this.
+  return true;
+#endif
+}
+
 }  // namespace
 
 // static
@@ -1264,13 +1287,9 @@ void Textfield::WriteDragDataForView(View* sender,
 
   SkBitmap bitmap;
   float raster_scale = ScaleFactorForDragFromWidget(GetWidget());
-  SkColor color = SK_ColorTRANSPARENT;
-#if defined(USE_X11)
-  // Fallback on the background color if the system doesn't support compositing.
-  if (!::features::IsUsingOzonePlatform() &&
-      !ui::XVisualManager::GetInstance()->ArgbVisualAvailable())
-    color = GetBackgroundColor();
-#endif
+  SkColor color = CanUseTransparentBackgroundForDragImage()
+                      ? SK_ColorTRANSPARENT
+                      : GetBackgroundColor();
   label.Paint(PaintInfo::CreateRootPaintInfo(
       ui::CanvasPainter(&bitmap, label.size(), raster_scale, color,
                         GetWidget()->GetCompositor()->is_pixel_canvas())