Allow creating GLImage-backed textures with glTexStorage2D.

gpu/command_buffer/build_gles2_cmd_buffer.py

Index: gpu/command_buffer/build_gles2_cmd_buffer.py
diff --git a/gpu/command_buffer/build_gles2_cmd_buffer.py b/gpu/command_buffer/build_gles2_cmd_buffer.py
index fc0f7fd4bfbc46c38ec738882504fcdc9ce8e18a..e7e7355ecffa36794b71d06f2660dc8bf135a680 100755
--- a/gpu/command_buffer/build_gles2_cmd_buffer.py
+++ b/gpu/command_buffer/build_gles2_cmd_buffer.py
@@ -1052,6 +1052,14 @@ _NAMED_TYPE_INFO = {
       'GL_TEXTURE_3D',
     ],
   },
+  'TextureBufferUsage': {
+    'type': 'GLenum',
+    'is_complete': True,
+    'valid': [
+      'GL_NONE',
+      'GL_TEXTURE_BUFFER_SCANOUT_CHROMIUM',
+    ],
+  },
   'TransformFeedbackBindTarget': {
     'type': 'GLenum',
     'valid': [
@@ -1474,6 +1482,7 @@ _NAMED_TYPE_INFO = {
       'GL_TEXTURE_MIN_FILTER',
       'GL_TEXTURE_WRAP_S',
       'GL_TEXTURE_WRAP_T',
+      'GL_TEXTURE_BUFFER_USAGE_CHROMIUM',

[Zhenyao Mo, 2017/06/20 00:14:30]

I am not sure this is the right thing to do. I think you need to add this
dynamically in FeatureInfo::Initialize() when you add the related extension.

For example, if it's WebGL contexts, since we removed many validation codes in
blink side, you don't want to leak this to WebGL.

     ],
     'valid_es3': [
       'GL_TEXTURE_BASE_LEVEL',