Change some more GMs to clear to opaque black, not transparent black.

N.B.: this will change results on the bots for all the tests modified.

BUG=skia:3319

Review URL: https://codereview.chromium.org/1077763002

gm/displacement.cpp

@@ -68,7 +68,7 @@ protected:
             make_bitmaps();
             fInitialized = true;
         }
-        canvas->clear(0x00000000);
+        canvas->clear(SK_ColorBLACK);
         SkPaint paint;
         SkAutoTUnref<SkImageFilter> displ(SkBitmapSource::Create(fCheckerboard));
         paint.setImageFilter(SkDisplacementMapEffect::Create(

gm/imagefiltersclipped.cpp

@@ -68,7 +68,7 @@ protected:
             this->make_gradient_circle(64, 64);
             fInitialized = true;
         }
-        canvas->clear(0x00000000);
+        canvas->clear(SK_ColorBLACK);
 
         SkAutoTUnref<SkImageFilter> gradient(SkBitmapSource::Create(fGradientCircle));
         SkAutoTUnref<SkImageFilter> checkerboard(SkBitmapSource::Create(fCheckerboard));

gm/imagefiltersscaled.cpp

@@ -68,7 +68,7 @@ protected:
             this->make_gradient_circle(64, 64);
             fInitialized = true;
         }
-        canvas->clear(0x00000000);
+        canvas->clear(SK_ColorBLACK);
 
         SkAutoTUnref<SkImageFilter> gradient(SkBitmapSource::Create(fGradientCircle));
         SkAutoTUnref<SkImageFilter> checkerboard(SkBitmapSource::Create(fCheckerboard));

gm/matrixconvolution.cpp

@@ -84,7 +84,7 @@ protected:
             make_bitmap();
             fInitialized = true;
         }
-        canvas->clear(0x00000000);
+        canvas->clear(SK_ColorBLACK);
         SkIPoint kernelOffset = SkIPoint::Make(1, 0);
         for (int x = 10; x < 310; x += 100) {
             this->draw(canvas, x, 10, kernelOffset, MCIF::kClamp_TileMode, true);

gm/matriximagefilter.cpp

@@ -58,7 +58,7 @@ protected:
     }
 
     virtual void onDraw(SkCanvas* canvas) {
-        canvas->clear(0x00000000);
+        canvas->clear(SK_ColorBLACK);
         SkMatrix matrix;
         SkScalar margin = SkIntToScalar(10);
         matrix.setSkew(SkDoubleToScalar(0.5), SkDoubleToScalar(0.2));

gm/offsetimagefilter.cpp

@@ -77,7 +77,7 @@ protected:
 
             fInitialized = true;
         }
-        canvas->clear(0x00000000);
+        canvas->clear(SK_ColorBLACK);
         SkPaint paint;
 
         for (int i = 0; i < 4; i++) {

gm/perlinnoise.cpp

@@ -58,7 +58,7 @@ protected:
     }
 
     virtual void onDraw(SkCanvas* canvas) {
-        canvas->clear(0x00000000);
+        canvas->clear(SK_ColorBLACK);
         test(canvas,   0,   0, SkPerlinNoiseShader::kFractalNoise_Type,
              0.1f, 0.1f, 0, 0, false);
         test(canvas, 100,   0, SkPerlinNoiseShader::kTurbulence_Type,

gm/resizeimagefilter.cpp

@@ -59,7 +59,7 @@ protected:
     }
 
     virtual void onDraw(SkCanvas* canvas) {
-        canvas->clear(0x00000000);
+        canvas->clear(SK_ColorBLACK);
 
         SkRect srcRect = SkRect::MakeWH(96, 96);
 

gm/tileimagefilter.cpp

@@ -56,7 +56,7 @@ protected:
 
             fInitialized = true;
         }
-        canvas->clear(0x00000000);
+        canvas->clear(SK_ColorBLACK);
 
         int x = 0, y = 0;
         for (size_t i = 0; i < 4; i++) {

gm/xfermodeimagefilter.cpp

@@ -74,7 +74,7 @@ protected:
     }
 
     void onDraw(SkCanvas* canvas) override {
-        canvas->clear(0x00000000);
+        canvas->clear(SK_ColorBLACK);
         SkPaint paint;
 
         const struct {