Implement SwiftShader fuzzer

Simply reuses the existing command buffer fuzzer, but with a SwiftShader backend.

Bug: swiftshader:51
Cq-Include-Trybots: master.tryserver.chromium.android:android_optional_gpu_tests_rel;master.tryserver.chromium.linux:linux_optional_gpu_tests_rel;master.tryserver.chromium.mac:mac_optional_gpu_tests_rel;master.tryserver.chromium.win:win_optional_gpu_tests_rel
Change-Id: I40f595c830f82c791033383d68f4b2802a35b8b2
Reviewed-on: https://chromium-review.googlesource.com/514246Reviewed-by: Geoff Lang <geofflang@chromium.org>
Commit-Queue: Antoine Labour <piman@chromium.org>
Cr-Commit-Position: refs/heads/master@{#478790}

gpu/BUILD.gn

@@ -471,4 +471,24 @@ if (is_linux) {
 
     libfuzzer_options = [ "max_len=16384" ]
   }
+
+  fuzzer_test("gpu_swiftshader_fuzzer") {
+    sources = [
+      "command_buffer/tests/fuzzer_main.cc",
+    ]
+
+    defines = [ "GPU_FUZZER_USE_SWIFTSHADER" ]
+
+    deps = [
+      ":gpu",
+      "//base",
+      "//base/third_party/dynamic_annotations",
+      "//gpu/command_buffer/common:gles2_utils",
+      "//ui/gfx/geometry",
+      "//ui/gl",
+      "//ui/gl:test_support",
+    ]
+
+    libfuzzer_options = [ "max_len=16384" ]
+  }
 }

gpu/command_buffer/tests/fuzzer_main.cc

@@ -49,7 +49,11 @@ const size_t kTransferBufferSize = 16384;
 const size_t kSmallTransferBufferSize = 16;
 const size_t kTinyTransferBufferSize = 3;
 
-#if !defined(GPU_FUZZER_USE_ANGLE)
+#if !defined(GPU_FUZZER_USE_ANGLE) && !defined(GPU_FUZZER_USE_SWIFTSHADER)
+#define GPU_FUZZER_USE_STUB
+#endif
+
+#if defined(GPU_FUZZER_USE_STUB)
 static const char kExtensions[] =
     "GL_AMD_compressed_ATC_texture "
     "GL_ANGLE_texture_compression_dxt3 "
@@ -109,19 +113,26 @@ class CommandBufferSetup {
                                     gl::kGLImplementationANGLEName);
     command_line->AppendSwitchASCII(switches::kUseANGLE,
                                     gl::kANGLEImplementationNullName);
-    gl::init::InitializeGLOneOffImplementation(gl::kGLImplementationEGLGLES2,
-                                               false, false, false);
+    CHECK(gl::init::InitializeGLOneOffImplementation(
+        gl::kGLImplementationEGLGLES2, false, false, false));
+#elif defined(GPU_FUZZER_USE_SWIFTSHADER)
+    command_line->AppendSwitchASCII(switches::kUseGL,
+                                    gl::kGLImplementationSwiftShaderName);
+    CHECK(gl::init::InitializeGLOneOffImplementation(
+        gl::kGLImplementationSwiftShaderGL, false, false, false));
+#endif
 
+#if !defined(GPU_FUZZER_USE_STUB)
     surface_ = new gl::PbufferGLSurfaceEGL(gfx::Size());
     surface_->Initialize();
     if (!recreate_context_) {
       InitContext();
     }
-#else
+#else   // defined(GPU_FUZZER_USE_STUB)
     surface_ = new gl::GLSurfaceStub;
     InitContext();
     gl::GLSurfaceTestSupport::InitializeOneOffWithMockBindings();
-#endif
+#endif  // defined(GPU_FUZZER_USE_STUB)
 
     translator_cache_ = new gles2::ShaderTranslatorCache(gpu_preferences_);
     completeness_cache_ = new gles2::FramebufferCompletenessCache;
@@ -161,7 +172,11 @@ class CommandBufferSetup {
     attrib_helper.alpha_size = 8;
     attrib_helper.depth_size = 0;
     attrib_helper.stencil_size = 0;
+#if defined(GPU_FUZZER_USE_SWIFTSHADER)
+    attrib_helper.context_type = gles2::CONTEXT_TYPE_OPENGLES2;
+#else
     attrib_helper.context_type = gles2::CONTEXT_TYPE_OPENGLES3;
+#endif
 
     bool result =
         decoder_->Initialize(surface_.get(), context_.get(), true,
@@ -232,7 +247,7 @@ class CommandBufferSetup {
   }
 
   void InitContext() {
-#if defined(GPU_FUZZER_USE_ANGLE)
+#if !defined(GPU_FUZZER_USE_STUB)
     context_ = new gl::GLContextEGL(share_group_.get());
     context_->Initialize(surface_.get(), gl::GLContextAttribs());
 #else