Request GL_ANGLE_texture_usage by default.

The validating command decoder exposes GL_ANGLE_texture_usage
unconditionally but the passthrough decoder did not because it had to be
requested first (for WebGL contexts). Request the extension at command
buffer initialization time.

BUG=1030835

Change-Id: I001f35650bd947eddf18878c56ac566c7dfd5588
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2023293Reviewed-by: Zhenyao Mo <zmo@chromium.org>
Commit-Queue: Geoff Lang <geofflang@chromium.org>
Cr-Commit-Position: refs/heads/master@{#736572}

gpu/command_buffer/service/gles2_cmd_decoder_passthrough.cc

@@ -929,6 +929,7 @@ gpu::ContextResult GLES2DecoderPassthroughImpl::Initialize(
       "GL_ANGLE_memory_size",
       "GL_ANGLE_native_id",
       "GL_ANGLE_texture_storage_external",
+      "GL_ANGLE_texture_usage",
       "GL_CHROMIUM_bind_uniform_location",
       "GL_CHROMIUM_sync_query",
       "GL_EXT_debug_marker",
@@ -958,7 +959,6 @@ gpu::ContextResult GLES2DecoderPassthroughImpl::Initialize(
           "GL_ANGLE_texture_compression_dxt1",
           "GL_ANGLE_texture_compression_dxt3",
           "GL_ANGLE_texture_compression_dxt5",
-          "GL_ANGLE_texture_usage",
           "GL_ANGLE_translated_shader_source",
           "GL_CHROMIUM_framebuffer_mixed_samples",
           "GL_CHROMIUM_path_rendering",