Remove Context::gatherParams.

This won't be used in the future. It saves a few instructions on each
entry point.

Also refactors a bit of touched code. Also adds in a missed entry
point: "glTexStorage2DMultisampleANGLE".

Removes related code and moves remaining helper code in params.h into a
new file entry_point_utils.h.

In total this patch series reduces overhead by up to 5%.

Bug: angleproject:2933
Change-Id: Ifb49564597cde6ba82dfc3e185227619fdc62612
Reviewed-on: https://chromium-review.googlesource.com/c/1299478
Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org>
Reviewed-by: Yuly Novikov <ynovikov@chromium.org>
Commit-Queue: Jamie Madill <jmadill@chromium.org>
diff --git a/src/libANGLE/Framebuffer.cpp b/src/libANGLE/Framebuffer.cpp
index 48249f3..08fb6b7 100644
--- a/src/libANGLE/Framebuffer.cpp
+++ b/src/libANGLE/Framebuffer.cpp
@@ -990,12 +990,10 @@
 
     if (mCachedStatus.value() == GL_FRAMEBUFFER_COMPLETE)
     {
-        Error err = syncState(context);
-        if (err.isError())
+        angle::Result err = syncState(context);
+        if (err != angle::Result::Continue())
         {
-            // TODO(jmadill): Remove when refactor complete. http://anglebug.com/2491
-            const_cast<Context *>(context)->handleError(err);
-            return GetDefaultReturnValue<EntryPoint::CheckFramebufferStatus, GLenum>();
+            return 0;
         }
         if (!mImpl->checkStatus(context))
         {