[Impeller] Fix string search in CompilerTest.SkSLTextureLookUpOrderOfOperations (#51109)

impeller/compiler/compiler_unittests.cc

diff --git a/impeller/compiler/compiler_unittests.cc b/impeller/compiler/compiler_unittests.cc
index 3e916ff..87e1344 100644
--- a/impeller/compiler/compiler_unittests.cc
+++ b/impeller/compiler/compiler_unittests.cc
@@ -135,11 +135,13 @@
       CanCompileAndReflect("texture_lookup.frag", SourceType::kFragmentShader));
 
   auto shader = GetShaderFile("texture_lookup.frag", GetParam());
-  auto string_mapping = reinterpret_cast<const char*>(shader->GetMapping());
+  std::string_view shader_mapping(
+      reinterpret_cast<const char*>(shader->GetMapping()), shader->GetSize());
 
-  EXPECT_TRUE(strcmp(string_mapping,
-                     "textureA.eval(textureA_size * ( vec2(1.0) + "
-                     "flutter_FragCoord.xy));") != -1);
+  constexpr std::string_view expected =
+      "textureA.eval(textureA_size * ( vec2(1.0) + flutter_FragCoord.xy));";
+
+  EXPECT_NE(shader_mapping.find(expected), std::string::npos);
 }
 
 TEST_P(CompilerTest, CanCompileStructs) {