Start enabling platform_canvas_unittests on Linux

These unittests have been disabled for years, limiting our coverage;
by implementing a Cairo version of DrawNativeRect() we can turn on at
least a few of them.

R=fmalita@chromium.org
BUG=154358

Review-Url: https://codereview.chromium.org/2332293003
Cr-Commit-Position: refs/heads/master@{#418545}

skia/BUILD.gn

@@ -662,7 +662,7 @@ test("skia_unittests") {
     "ext/skia_utils_mac_unittest.mm",
   ]
 
-  if (!is_win && !is_mac) {
+  if (!is_win && !is_mac && !use_cairo) {
     sources -= [ "ext/platform_canvas_unittest.cc" ]
   }
 
@@ -684,6 +684,12 @@ test("skia_unittests") {
       "//skia/public/interfaces:test_interfaces",
     ]
   }
+
+  if (is_linux) {
+    if (use_pango) {
+      configs += [ "//build/config/linux/pangocairo" ]
+    }
+  }
 }
 
 if (!is_ios) {

skia/ext/platform_canvas_unittest.cc

@@ -26,6 +26,14 @@
 #include <unistd.h>
 #endif
 
+#if defined(USE_CAIRO)
+#if defined(OS_OPENBSD)
+#include <cairo.h>
+#else
+#include <cairo/cairo.h>
+#endif  // OS_OPENBSD
+#endif  // USE_CAIRO
+
 namespace skia {
 
 namespace {
@@ -116,12 +124,10 @@ bool VerifyBlackRect(const SkCanvas& canvas, int x, int y, int w, int h) {
   return VerifyRect(canvas, SK_ColorWHITE, SK_ColorBLACK, x, y, w, h);
 }
 
-#if !defined(USE_AURA)  // http://crbug.com/154358
 // Check that every pixel in the canvas is a single color.
 bool VerifyCanvasColor(const SkCanvas& canvas, uint32_t canvas_color) {
   return VerifyRect(canvas, canvas_color, 0, 0, 0, 0, 0);
 }
-#endif  // !defined(USE_AURA)
 
 #if defined(OS_WIN)
 void DrawNativeRect(SkCanvas& canvas, int x, int y, int w, int h) {
@@ -147,6 +153,15 @@ void DrawNativeRect(SkCanvas& canvas, int x, int y, int w, int h) {
   CGColorRelease(black);
   CGContextFillRect(context, inner_rc);
 }
+#elif defined(USE_CAIRO)
+void DrawNativeRect(SkCanvas& canvas, int x, int y, int w, int h) {
+  skia::ScopedPlatformPaint scoped_platform_paint(&canvas);
+  cairo_t* context = scoped_platform_paint.GetPlatformSurface();
+
+  cairo_rectangle(context, x, y, w, h);
+  cairo_set_source_rgb(context, 0.0, 0.0, 0.0);
+  cairo_fill(context);
+}
 #else
 void DrawNativeRect(SkCanvas& canvas, int x, int y, int w, int h) {
   NOTIMPLEMENTED();
@@ -225,7 +240,6 @@ TEST(PlatformCanvas, SkLayer) {
   EXPECT_TRUE(VerifyBlackRect(*canvas, kLayerX, kLayerY, kLayerW, kLayerH));
 }
 
-#if !defined(USE_AURA)  // http://crbug.com/154358
 // Test native clipping.
 TEST(PlatformCanvas, ClipRegion) {
   // Initialize a white canvas
@@ -250,7 +264,6 @@ TEST(PlatformCanvas, ClipRegion) {
   }
   EXPECT_TRUE(VerifyCanvasColor(*canvas, SK_ColorWHITE));
 }
-#endif  // !defined(USE_AURA)
 
 // Test the layers get filled properly by native rendering.
 TEST(PlatformCanvas, FillLayer) {