ui: Remove some cruft related to cairo rendering

This is dead code as cairo is no longer used.

No functional change.

Change-Id: I7d7f207d604de8c8f9bbf1098b7ecb1f91fa5685
Reviewed-on: https://chromium-review.googlesource.com/755656Reviewed-by: danakj <danakj@chromium.org>
Commit-Queue: Michael Spang <spang@chromium.org>
Cr-Commit-Position: refs/heads/master@{#515042}

ui/gfx/BUILD.gn

@@ -2,7 +2,6 @@
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
-import("//build/config/linux/pangocairo/pangocairo.gni")
 import("//build/config/ui.gni")
 import("//device/vr/features/features.gni")
 import("//testing/test.gni")
@@ -219,7 +218,6 @@ component("gfx") {
       "skia_paint_util.cc",
       "skia_paint_util.h",
     ]
-    deps += [ "//build/config/linux/pangocairo:features" ]
   }
 
   configs += [
@@ -387,10 +385,6 @@ component("gfx") {
     sources -= [ "path_x11.cc" ]
   }
 
-  if (use_pangocairo) {
-    configs += [ "//build/config/linux/pangocairo" ]
-  }
-
   if (is_fuchsia) {
     sources += [
       "font_fallback_fuchsia.cc",

ui/gfx/canvas.cc

@@ -9,7 +9,6 @@
 
 #include "base/i18n/rtl.h"
 #include "base/logging.h"
-#include "build/config/linux/pangocairo/features.h"
 #include "cc/paint/paint_flags.h"
 #include "cc/paint/paint_shader.h"
 #include "third_party/skia/include/core/SkBitmap.h"
@@ -36,13 +35,6 @@ Canvas::Canvas(const Size& size, float image_scale, bool is_opaque)
   Size pixel_size = ScaleToCeiledSize(size, image_scale);
   canvas_ = CreateOwnedCanvas(pixel_size, is_opaque);
 
-#if !BUILDFLAG(USE_PANGOCAIRO)
-  // skia::PlatformCanvas instances are initialized to 0 by Cairo, but
-  // uninitialized on other platforms.
-  if (!is_opaque)
-    canvas_->clear(SkColorSetARGB(0, 0, 0, 0));
-#endif
-
   SkScalar scale_scalar = SkFloatToScalar(image_scale);
   canvas_->scale(scale_scalar, scale_scalar);
 }

ui/gfx/native_widget_types.h

@@ -91,8 +91,6 @@ struct NSView;
 class NSWindow;
 class NSTextField;
 #endif  // __OBJC__
-#elif defined(OS_POSIX)
-typedef struct _cairo cairo_t;
 #endif
 
 #if defined(OS_ANDROID)