Use SwiftShader and ANGLE for RasterDecoder fuzzing

This will hopefully catch issues where RasterDecoder instructs the
driver to make bad memory accesses (e.g. glTexImage2D with data =
nullptr and GL_PIXEL_UNPACK_BUFFER set inappropriately). The current
gpu_raster_fuzzer target uses a stub GL implementation and won't catch
these errors.

Bug: 856208
Cq-Include-Trybots: luci.chromium.try:android_optional_gpu_tests_rel;luci.chromium.try:linux_optional_gpu_tests_rel;luci.chromium.try:mac_optional_gpu_tests_rel;luci.chromium.try:win_optional_gpu_tests_rel
Change-Id: Iea7dac66ef051a82af38ca2dde3e8374187f21ba
Reviewed-on: https://chromium-review.googlesource.com/1125141
Commit-Queue: Jonathan Backer <backer@chromium.org>
Reviewed-by: Zhenyao Mo <zmo@chromium.org>
Cr-Commit-Position: refs/heads/master@{#572600}

gpu/BUILD.gn

@@ -663,4 +663,50 @@ if (is_linux) {
 
     libfuzzer_options = [ "max_len=16384" ]
   }
+
+  fuzzer_test("gpu_raster_swiftshader_fuzzer") {
+    sources = [
+      "command_buffer/tests/fuzzer_main.cc",
+    ]
+
+    defines = [
+      "GPU_FUZZER_USE_RASTER_DECODER",
+      "GPU_FUZZER_USE_SWIFTSHADER",
+    ]
+
+    deps = [
+      ":gles2",
+      ":gpu",
+      "//base",
+      "//base/third_party/dynamic_annotations",
+      "//ui/gfx/geometry",
+      "//ui/gl",
+      "//ui/gl:test_support",
+    ]
+
+    libfuzzer_options = [ "max_len=16384" ]
+  }
+
+  fuzzer_test("gpu_raster_angle_fuzzer") {
+    sources = [
+      "command_buffer/tests/fuzzer_main.cc",
+    ]
+
+    defines = [
+      "GPU_FUZZER_USE_RASTER_DECODER",
+      "GPU_FUZZER_USE_ANGLE",
+    ]
+
+    deps = [
+      ":gles2",
+      ":gpu",
+      "//base",
+      "//base/third_party/dynamic_annotations",
+      "//ui/gfx/geometry",
+      "//ui/gl",
+      "//ui/gl:test_support",
+    ]
+
+    libfuzzer_options = [ "max_len=16384" ]
+  }
 }