Revert of Repurpose Release_Developer BUILDTYPE and remove SK_DEVELOPER.

site/dev/runtime/index.md

 Runtime Configuration
 =====================
 
 Skia supports the configuration of various aspects of its behavior at runtime,
 allowing developers to enable\/disable features, or to experiment with numerical
 quantities without recompiling.
 
 ## Enabling runtime configuration
 
 In order to use a runtime-configurable variable in your source, simply:
@@ skipping 134 matching lines @@
 line will be commented out and have its value already equal to its default, so
 you can then edit this file to your liking.
 
 To trigger this behavior, call the function
 `skRTConfRegistry().possiblyDumpFile(); ` or simply use `SkAutoGraphics
 ag;`, which also validates your configuration and print out active non-default
 options.
 
 ## Are these things enabled all the time?
 
-No, they are only enabled in builds where SK_DEBUG is defined. This includes both
-`Debug` and `Release_Developer` gyp BUILDTYPES. The `Release_Developer` build type
-has exactly the same build flags as `Release`, except it re-enables SK_DEBUG, which
-in turn enables runtime configuration behavior.
+In `Debug` builds, yes. `Release` builds disable runtime configuration by
+default, but it is still useful to be able to tweak certain algorithm parameters
+at runtime to do scripted performance studies. Therefore, a third build type,
+`Release_Developer` has been added. This build type has exactly the same build
+flags as `Release`, except it re-enables all runtime configuration behavior.
 Specifically:
 
 <!--?prettify?-->
 ~~~~
 prompt% ninja -C BUILDTYPE=Release_Developer
 ~~~~
 
 ... wait a long time ...
 
 <!--?prettify?-->
 ~~~~
 prompt % skia_gpu_printShaders=true out/Release_Developer/dm
 ~~~~
 
 ... enjoy ...
 
 ## Known issues / limitations
 
 Lines in 'skia.conf', including comments, are limited to 1024 characters.
 Runtime configuration variables of type `char \* ` cannot currently have spaces
 in them.
 Runtime variables are only fully supported for `int`, `unsigned int`, `float`,
 `double`, `bool`, and `char \*`.
+
+## Questions?  Bugs?  Improvements?
+
+Feel free to send feedback on this system to Greg Humphreys \(humper@google\.com\)