Add config options to run different GPU APIs to dm and nanobench

Add extended config specification form that can be used to run different
gpu backend with different APIs.

The configs can be specified with the form:
gpu(api=string,dit=bool,nvpr=bool,samples=int)

This replaces and removes the --gpuAPI flag.

All existing configs should still work.

Adds following documentation:

out/Debug/dm --help config

Flags:
    --config:	type: string	default: 565 8888 gpu nonrendering
        Options: 565 8888 debug gpu gpudebug gpudft gpunull msaa16 msaa4
        nonrendering null nullgpu nvprmsaa16 nvprmsaa4 pdf pdf_poppler skp svg
        xps or use extended form 'backend(option=value,...)'.

        Extended form: 'backend(option=value,...)'

        Possible backends and options:

        gpu(api=string,dit=bool,nvpr=bool,samples=int)	GPU backend
        	api	type: string	default: native.
        	    Select graphics API to use with gpu backend.
        	    Options:
        		native			Use platform default OpenGL or OpenGL ES backend.
        		gl    			Use OpenGL.
        		gles  			Use OpenGL ES.
        		debug 			Use debug OpenGL.
        		null  			Use null OpenGL.
        	dit	type: bool	default: false.
        	    Use device independent text.
        	nvpr	type: bool	default: false.
        	    Use NV_path_rendering OpenGL and OpenGL ES extension.
        	samples	type: int	default: 0.
        	    Use multisampling with N samples.

        Predefined configs:

        	gpu      	= gpu()
        	msaa4    	= gpu(samples=4)
        	msaa16   	= gpu(samples=16)
        	nvprmsaa4	= gpu(nvpr=true,samples=4)
        	nvprmsaa16	= gpu(nvpr=true,samples=16)
        	gpudft    	= gpu(dit=true)
        	gpudebug  	= gpu(api=debug)
        	gpunull   	= gpu(api=null)
        	debug     	= gpu(api=debug)
        	nullgpu   	= gpu(api=null)

BUG=skia:2992

Committed: https://skia.googlesource.com/skia/+/e13ca329fca4c28cf4e078561f591ab27b743d23
GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1490113005

Committed: https://skia.googlesource.com/skia/+/c8b4336444e7b90382e04e33665fb3b8490b825b

Review URL: https://codereview.chromium.org/1490113005

3 files changed, 18 insertions, 9 deletions

diff --git a/include/gpu/gl/SkNullGLContext.h b/include/gpu/gl/SkNullGLContext.h
index 1f63438264..9e799a9fea 100644
--- a/include/gpu/gl/SkNullGLContext.h
+++ b/include/gpu/gl/SkNullGLContext.h
@@ -14,7 +14,12 @@ class SK_API SkNullGLContext : public SkGLContext {
 public:
     ~SkNullGLContext() override;
 
-    static SkNullGLContext* Create(GrGLStandard);
+    static SkNullGLContext* Create();
+    // FIXME: remove once Chromium has been updated.
+    static SkNullGLContext* Create(GrGLStandard forcedAPI) {
+        SkASSERT(forcedAPI == kNone_GrGLStandard);
+        (void)forcedAPI;        return Create();
+    }
 
     class ContextState;
 
diff --git a/include/gpu/gl/angle/SkANGLEGLContext.h b/include/gpu/gl/angle/SkANGLEGLContext.h
index 7858fff964..ea5e877ca2 100644
--- a/include/gpu/gl/angle/SkANGLEGLContext.h
+++ b/include/gpu/gl/angle/SkANGLEGLContext.h
@@ -15,18 +15,25 @@
 class SkANGLEGLContext : public SkGLContext {
 public:
     ~SkANGLEGLContext() override;
-
-    static SkANGLEGLContext* Create(GrGLStandard forcedGpuAPI, bool useGLBackend) {
-        if (kGL_GrGLStandard == forcedGpuAPI) {
+#ifdef SK_BUILD_FOR_WIN
+    static SkANGLEGLContext* CreateDirectX() {
+        SkANGLEGLContext* ctx = new SkANGLEGLContext(false);
+        if (!ctx->isValid()) {
+            delete ctx;
             return NULL;
         }
-        SkANGLEGLContext* ctx = new SkANGLEGLContext(useGLBackend);
+        return ctx;
+    }
+#endif
+    static SkANGLEGLContext* CreateOpenGL() {
+        SkANGLEGLContext* ctx = new SkANGLEGLContext(true);
         if (!ctx->isValid()) {
             delete ctx;
             return NULL;
         }
         return ctx;
     }
+
     GrEGLImage texture2DToEGLImage(GrGLuint texID) const override;
     void destroyEGLImage(GrEGLImage) const override;
     GrGLuint eglImageToExternalTexture(GrEGLImage) const override;
diff --git a/include/gpu/gl/command_buffer/SkCommandBufferGLContext.h b/include/gpu/gl/command_buffer/SkCommandBufferGLContext.h
index 7fece3c83c..47f3fd967a 100644
--- a/include/gpu/gl/command_buffer/SkCommandBufferGLContext.h
+++ b/include/gpu/gl/command_buffer/SkCommandBufferGLContext.h
@@ -16,10 +16,7 @@ class SkCommandBufferGLContext : public SkGLContext {
 public:
     ~SkCommandBufferGLContext() override;
 
-    static SkCommandBufferGLContext* Create(GrGLStandard forcedGpuAPI) {
-        if (kGL_GrGLStandard == forcedGpuAPI) {
-            return nullptr;
-        }
+    static SkCommandBufferGLContext* Create() {
         SkCommandBufferGLContext* ctx = new SkCommandBufferGLContext;
         if (!ctx->isValid()) {
             delete ctx;