Remove skia::SupportsPlatformPaint()

It is equivalent to checking the result of GetNativeDrawingContext(), so
do that instead, in NativeThemeWin::Paint().

Also remove an unused param of NativeThemeWin::PaintIndirect().

BUG=675977
R=reed@google.com

Review-Url: https://codereview.chromium.org/2610003002
Cr-Commit-Position: refs/heads/master@{#441388}

skia/ext/platform_canvas.cc

@@ -58,10 +58,6 @@ bool GetWritablePixels(SkCanvas* canvas, SkPixmap* result) {
   return true;
 }
 
-bool SupportsPlatformPaint(const SkCanvas* canvas) {
-  return GetPlatformDevice(canvas->getTopDevice(true)) != nullptr;
-}
-
 size_t PlatformCanvasStrideForWidth(unsigned width) {
   return 4 * width;
 }

skia/ext/platform_canvas.h

@@ -121,11 +121,6 @@ SK_API SkBitmap ReadPixels(SkCanvas* canvas);
 // the pixmap to empty.
 SK_API bool GetWritablePixels(SkCanvas* canvas, SkPixmap* pixmap);
 
-// Returns true if native platform routines can be used to draw on the
-// given canvas. If this function returns false,
-// GetNativeDrawingContext() should return NULL.
-SK_API bool SupportsPlatformPaint(const SkCanvas* canvas);
-
 // Returns the NativeDrawingContext to use for native platform drawing calls.
 SK_API NativeDrawingContext GetNativeDrawingContext(SkCanvas* canvas);
 

ui/native_theme/native_theme_win.cc

@@ -285,10 +285,10 @@ void NativeThemeWin::Paint(SkCanvas* canvas,
   // UI features like scrollbars. However, we need to set up that buffer,
   // and then read it back when it's done and blit it onto the screen.
 
-  if (skia::SupportsPlatformPaint(canvas))
+  if (surface)
     PaintDirect(canvas, surface, part, state, rect, extra);
   else
-    PaintIndirect(canvas, surface, part, state, rect, extra);
+    PaintIndirect(canvas, part, state, rect, extra);
 }
 
 NativeThemeWin::NativeThemeWin()
@@ -673,7 +673,6 @@ SkColor NativeThemeWin::GetSystemColor(ColorId color_id) const {
 }
 
 void NativeThemeWin::PaintIndirect(SkCanvas* destination_canvas,
-                                   HDC destination_hdc,
                                    Part part,
                                    State state,
                                    const gfx::Rect& rect,

ui/native_theme/native_theme_win.h

@@ -144,7 +144,6 @@ class NATIVE_THEME_EXPORT NativeThemeWin : public NativeTheme,
   // temporary HDC, and then blit the result to canvas.  This is to work around
   // the fact that Windows XP and some classic themes give bogus alpha values.
   void PaintIndirect(SkCanvas* destination_canvas,
-                     HDC destination_hdc,
                      Part part,
                      State state,
                      const gfx::Rect& rect,