Hook ANGLE_request_extension up to the passthrough cmd decoder.

third_party/WebKit/Source/modules/webgl/WebGLDrawBuffers.cpp

Index: third_party/WebKit/Source/modules/webgl/WebGLDrawBuffers.cpp
diff --git a/third_party/WebKit/Source/modules/webgl/WebGLDrawBuffers.cpp b/third_party/WebKit/Source/modules/webgl/WebGLDrawBuffers.cpp
index dd5047330e1f78625ce29b75a3d7a95f2df2d702..097549c63650c333ddc9c7311cd524cd53ae5909 100644
--- a/third_party/WebKit/Source/modules/webgl/WebGLDrawBuffers.cpp
+++ b/third_party/WebKit/Source/modules/webgl/WebGLDrawBuffers.cpp
@@ -102,6 +102,12 @@ bool WebGLDrawBuffers::satisfiesWebGLRequirements(
   gpu::gles2::GLES2Interface* gl = webglContext->contextGL();
   Extensions3DUtil* extensionsUtil = webglContext->extensionsUtil();
 
+  if (!extensionsUtil->isExtensionEnabled("GL_EXT_draw_buffers")) {
+    // Extension can be enabled but is not yet so we trust that the command
+    // decoder has full support
+    return true;

[Zhenyao Mo, 2017/02/06 22:31:38]

So when we actually try to enable this extension, this function may return
false. Will this cause problems?

[Geoff Lang, 2017/02/07 19:01:15]

The comment below says that we can only get here if GL_EXT_draw_buffers is
supported but it's not very clear that it can be supported but not enabled yet. 
I added a new method to Extensions3DUtil, isExtensionRequestable, to make it
more readable.

+  }
+
   // This is called after we make sure GL_EXT_draw_buffers is supported.
   GLint maxDrawBuffers = 0;
   GLint maxColorAttachments = 0;