Add a frontend feature to disable anisotropic filtering.

This allows us to disable support for GL_EXT_texture_filter_anisotropic
at runtime and make performance comparisons.

Bug: b/167404532
Change-Id: Id80458e7f116e195366432fe73e8e776e9a3047b
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2278024
Commit-Queue: Geoff Lang <geofflang@chromium.org>
Reviewed-by: Courtney Goeltzenleuchter <courtneygo@google.com>
Reviewed-by: Tim Van Patten <timvp@google.com>

include/platform/FrontendFeatures.h

@@ -54,6 +54,12 @@ struct FrontendFeatures : angle::FeatureSetBase
     angle::Feature disableProgramBinary = {
         "disable_program_binary", angle::FeatureCategory::FrontendFeatures,
         "Disable support for GL_OES_get_program_binary", &members, "http://anglebug.com/5007"};
+
+    // Allow disabling of GL_EXT_texture_filter_anisotropic through a runtime feature for
+    // performance comparisons.
+    angle::Feature disableAnisotropicFiltering = {
+        "disable_anisotropic_filtering", angle::FeatureCategory::FrontendWorkarounds,
+        "Disable support for anisotropic filtering", &members};
 };
 
 inline FrontendFeatures::FrontendFeatures()  = default;

src/libANGLE/Context.cpp

@@ -3209,6 +3209,11 @@ Extensions Context::generateSupportedExtensions() const
         supportedExtensions.colorBufferFloatRGBA = false;
     }
 
+    if (getFrontendFeatures().disableAnisotropicFiltering.enabled)
+    {
+        supportedExtensions.textureFilterAnisotropic = false;
+    }
+
     // Some extensions are always available because they are implemented in the GL layer.
     supportedExtensions.bindUniformLocation   = true;
     supportedExtensions.vertexArrayObjectOES  = true;