Check If ImageBuffer is allocated before proceeding.

Source/platform/graphics/GraphicsContextTest.cpp

Index: Source/platform/graphics/GraphicsContextTest.cpp
diff --git a/Source/platform/graphics/GraphicsContextTest.cpp b/Source/platform/graphics/GraphicsContextTest.cpp
index 3672c36bdec4e4fec1f806b988eaa5a4248756d9..f862cf2b5c5df7e1cce618ce47dd423e616352fb 100644
--- a/Source/platform/graphics/GraphicsContextTest.cpp
+++ b/Source/platform/graphics/GraphicsContextTest.cpp
@@ -243,6 +243,7 @@ TEST(GraphicsContextTest, trackImageMask)
     context.beginTransparencyLayer(1);
 
     OwnPtr<ImageBuffer> alphaImage = ImageBuffer::create(IntSize(100, 100));
+    EXPECT_FALSE(!alphaImage);
     alphaImage->context()->fillRect(IntRect(0, 0, 100, 100), alpha);
 
     context.setCompositeOperation(CompositeSourceOver);
@@ -280,6 +281,7 @@ TEST(GraphicsContextTest, trackImageMaskWithOpaqueRect)
     context.beginTransparencyLayer(1);
 
     OwnPtr<ImageBuffer> alphaImage = ImageBuffer::create(IntSize(100, 100));
+    EXPECT_FALSE(!alphaImage);
     alphaImage->context()->fillRect(IntRect(0, 0, 100, 100), alpha);
 
     context.setCompositeOperation(CompositeSourceOver);