Fix SkShader leak for Gradient VectorDrawable and test

This CL fixes a SkShader leak in VD when applying local matrix
to the shader. Specifically, the usage of newWithLocalMatrix(...)
increments the shader's ref count in every draw() call for
Gradient VectorDrawable, whereas there's no balancing call to
decrement the ref count in draw(). In this CL, we assume
the ownership of the shader returned from newWithLocalMatrix(...)
to ensure the correct ref count management.

Also, add test to verify that shader is no longer being leaked

BUG: 32067647
Test: this CL

Change-Id: Ic15fe46cde06a73d81b44e2d3c56b51907344cc0

libs/hwui/VectorDrawable.cpp

@@ -202,7 +202,9 @@ void FullPath::drawPath(SkCanvas* outCanvas, SkPath& renderPath, float strokeSca
     if (properties.getFillGradient() != nullptr) {
         paint.setColor(applyAlpha(SK_ColorBLACK, properties.getFillAlpha()));
         SkShader* newShader = properties.getFillGradient()->newWithLocalMatrix(matrix);
-        paint.setShader(newShader);
+        // newWithLocalMatrix(...) creates a new SkShader and returns a bare pointer. We need to
+        // remove the extra ref so that the ref count is correctly managed.
+        paint.setShader(newShader)->unref();
         needsFill = true;
     } else if (properties.getFillColor() != SK_ColorTRANSPARENT) {
         paint.setColor(applyAlpha(properties.getFillColor(), properties.getFillAlpha()));
@@ -222,7 +224,9 @@ void FullPath::drawPath(SkCanvas* outCanvas, SkPath& renderPath, float strokeSca
     if (properties.getStrokeGradient() != nullptr) {
         paint.setColor(applyAlpha(SK_ColorBLACK, properties.getStrokeAlpha()));
         SkShader* newShader = properties.getStrokeGradient()->newWithLocalMatrix(matrix);
-        paint.setShader(newShader);
+        // newWithLocalMatrix(...) creates a new SkShader and returns a bare pointer. We need to
+        // remove the extra ref so that the ref count is correctly managed.
+        paint.setShader(newShader)->unref();
         needsStroke = true;
     } else if (properties.getStrokeColor() != SK_ColorTRANSPARENT) {
         paint.setColor(applyAlpha(properties.getStrokeColor(), properties.getStrokeAlpha()));

libs/hwui/tests/unit/VectorDrawableTests.cpp

@@ -426,5 +426,49 @@ TEST(VectorDrawable, groupProperties) {
     EXPECT_EQ(1.0f, properties->getPivotY());
 
 }
+
+static SkShader* createShader(bool* isDestroyed) {
+    class TestShader : public SkShader {
+    public:
+        TestShader(bool* isDestroyed) : SkShader(), mDestroyed(isDestroyed) {
+        }
+        ~TestShader() {
+            *mDestroyed = true;
+        }
+
+        Factory getFactory() const override { return nullptr; }
+    private:
+        bool* mDestroyed;
+    };
+    return new TestShader(isDestroyed);
+}
+
+TEST(VectorDrawable, drawPathWithoutIncrementingShaderRefCount) {
+    VectorDrawable::FullPath path("m1 1", 4);
+    SkBitmap bitmap;
+    SkImageInfo info = SkImageInfo::Make(5, 5, kN32_SkColorType, kPremul_SkAlphaType);
+    bitmap.setInfo(info);
+    bitmap.allocPixels(info);
+    SkCanvas canvas(bitmap);
+
+    bool shaderIsDestroyed = false;
+
+    // Initial ref count is 1
+    SkShader* shader = createShader(&shaderIsDestroyed);
+
+    // Setting the fill gradient increments the ref count of the shader by 1
+    path.mutateStagingProperties()->setFillGradient(shader);
+    path.draw(&canvas, SkMatrix::I(), 1.0f, 1.0f, true);
+    // Resetting the fill gradient decrements the ref count of the shader by 1
+    path.mutateStagingProperties()->setFillGradient(nullptr);
+
+    // Expect ref count to be 1 again, i.e. nothing else to have a ref to the shader now. Unref()
+    // again should bring the ref count to zero and consequently trigger detor.
+    shader->unref();
+
+    // Verify that detor is called.
+    EXPECT_TRUE(shaderIsDestroyed);
+}
+
 }; // namespace uirenderer
 }; // namespace android