Use ErrorStream everywhere

Eliminates one more usage of FormatString and its static initializer.

Add more ErrorStream types
and replace gl::Error and egl::Error with them.

BUG=angleproject:1644

Change-Id: Ib498d0ae4b81a332ec71aed7cf709993b154e6bb
Reviewed-on: https://chromium-review.googlesource.com/505429
Commit-Queue: Yuly Novikov <ynovikov@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
diff --git a/src/libANGLE/Context.cpp b/src/libANGLE/Context.cpp
index 479ef92..cc5a005 100644
--- a/src/libANGLE/Context.cpp
+++ b/src/libANGLE/Context.cpp
@@ -118,7 +118,7 @@
         }
         default:
             UNREACHABLE();
-            return gl::Error(GL_INVALID_OPERATION, "Unreachable Error");
+            return gl::InternalError() << "Unreachable Error";
     }
 }
 
@@ -4099,9 +4099,9 @@
 {
     if (!mScratchBuffer.get(requestedSize, scratchBufferOut))
     {
-        return gl::OutOfMemory() << "Failed to allocate internal buffer.";
+        return OutOfMemory() << "Failed to allocate internal buffer.";
     }
-    return gl::NoError();
+    return NoError();
 }
 
 void Context::dispatchCompute(GLuint numGroupsX, GLuint numGroupsY, GLuint numGroupsZ)