Add EXT_color_buffer_half_float extension support in GPU commandbuffer service.

ui/gl/gl_gl_api_implementation.cc

Index: ui/gl/gl_gl_api_implementation.cc
diff --git a/ui/gl/gl_gl_api_implementation.cc b/ui/gl/gl_gl_api_implementation.cc
index 802d250a37b65856943ec6cfad9a5465ea6986ad..f76ccab8a645a99affdbea94278dec6a573755b8 100644
--- a/ui/gl/gl_gl_api_implementation.cc
+++ b/ui/gl/gl_gl_api_implementation.cc
@@ -125,6 +125,14 @@ static void GL_BINDING_CALL CustomTexStorage2DEXT(
       target, levels, gl_internal_format, width, height);
 }
 
+static void GL_BINDING_CALL CustomReadPixels(
+    GLint x, GLint y, GLsizei width, GLsizei height, GLenum format,
+    GLenum type, void* pixels) {
+  GLenum gl_type = GetTexType(type);
+  return g_driver_gl.orig_fn.glReadPixelsFn(
+      x, y, width, height, format, gl_type, pixels);
+}
+
 }  // anonymous namespace
 
 void DriverGL::Initialize() {
@@ -140,6 +148,8 @@ void DriverGL::InitializeExtensions(GLContext* context) {
       reinterpret_cast<glTexSubImage2DProc>(CustomTexSubImage2D);
   fn.glTexStorage2DEXTFn =
       reinterpret_cast<glTexStorage2DEXTProc>(CustomTexStorage2DEXT);
+  fn.glReadPixelsFn =
+      reinterpret_cast<glReadPixelsProc>(CustomReadPixels);
 }
 
 void InitializeGLBindingsGL() {