Do not build the ktx encoder for android framework

Move SkKTXImageEncoder.cpp into an optional block, and disable that
block for the android framework. Use a new define to determine whether
to define the entry point, rather than using
SK_BUILD_FOR_ANDROID_FRAMEWORK.

Change-Id: I41103459135af744cf5715f27783c63dc37a7ad1
Reviewed-on: https://skia-review.googlesource.com/5982
Commit-Queue: Leon Scroggins <scroggo@google.com>
Commit-Queue: Mike Klein <mtklein@chromium.org>
Reviewed-by: Mike Klein <mtklein@chromium.org>

BUILD.gn

@@ -27,6 +27,7 @@ declare_args() {
 
   skia_enable_android_framework_defines = false
   skia_enable_gpu = true
+  skia_enable_ktx_encoder = true
   skia_enable_tools = is_skia_standalone
   skia_enable_vulkan_debug_layers = is_skia_standalone && is_debug
   skia_vulkan_sdk = getenv("VULKAN_SDK")
@@ -430,6 +431,14 @@ optional("jpeg") {
   ]
 }
 
+optional("ktx_encoder") {
+  enabled = skia_enable_ktx_encoder
+  public_defines = [ "SK_HAS_KTX_ENCODER" ]
+  sources = [
+    "src/images/SkKTXImageEncoder.cpp",
+  ]
+}
+
 optional("pdf") {
   enabled = skia_use_zlib
 
@@ -536,6 +545,7 @@ component("skia") {
     ":gpu",
     ":hsw",
     ":jpeg",
+    ":ktx_encoder",
     ":none",
     ":pdf",
     ":png",
@@ -578,7 +588,6 @@ component("skia") {
     "src/codec/SkSwizzler.cpp",
     "src/codec/SkWbmpCodec.cpp",
     "src/images/SkImageEncoder.cpp",
-    "src/images/SkKTXImageEncoder.cpp",
     "src/ports/SkDiscardableMemory_none.cpp",
     "src/ports/SkGlobalInitialization_default.cpp",
     "src/ports/SkImageGenerator_skia.cpp",

gn/gn_to_bp.py

@@ -109,6 +109,7 @@ cc_library {
 
 # We'll run GN to get the main source lists and include directories for Skia.
 gn_args = {
+  'skia_enable_ktx_encoder':         'false',
   'skia_enable_vulkan_debug_layers': 'false',
   'skia_use_system_expat':           'true',
   'skia_use_vulkan':                 'true',

src/images/SkImageEncoderPriv.h

@@ -28,7 +28,7 @@
     #define SkEncodeImageAsWEBP(...) false
 #endif
 
-#ifndef SK_BUILD_FOR_ANDROID_FRAMEWORK
+#ifdef SK_HAS_KTX_ENCODER
     bool SkEncodeImageAsKTX(SkWStream*, const SkPixmap&);
 #else
     #define SkEncodeImageAsKTX(...) false