skia: Add support for CHROMIUM_image backed textures.

include/gpu/GrTypes.h

Index: include/gpu/GrTypes.h
diff --git a/include/gpu/GrTypes.h b/include/gpu/GrTypes.h
index dbcb9a6583321d715a437a9982c7da7b5521066e..c8f4ae377f645a965060f780084456eef9e0e67b 100644
--- a/include/gpu/GrTypes.h
+++ b/include/gpu/GrTypes.h
@@ -409,6 +409,45 @@ enum GrSurfaceFlags {
 
 GR_MAKE_BITFIELD_OPS(GrSurfaceFlags)
 
+// opaque type for 3D API object handles
+typedef intptr_t GrBackendObject;
+
+/**
+ * An abstract base class which consumers of Skia can subclass and pass to Skia.
+ * Skia will use this object in place of its backend API texture creation
+ * function.
+ */
+class GrTextureStorageAllocator {
+public:
+    /*
+     * Whether a texture can be created with the given pixel config.
+     */
+    virtual bool supportsPixelConfig(GrPixelConfig config) = 0;
+    /*
+     * Generates and binds a texture to |textureStorageTarget()|. Allocates
+     * storage for the texture.
+     *
+     * The MIN and MAX filters for the created texture must be GL_LINEAR. The
+     * WRAP_S and WRAP_T must be GL_CLAMP_TO_EDGE.
+     *
+     * The internal format must be GL_RGBA.

[bsalomon, 2016/01/29 16:57:38]

I'm not crazy about this restriction. I get that that's all that will be
supported for the initial subclass in Chromium, but I'd like to use this for
some testing on the Skia side and would like to allow support for all formats. I
think that would mean that the Allocator can fail and allow the default
implementation to take over.

Also, I think for certain potential use cases the allocator should at least have
the option of performing the upload, in case it can do something more efficient
than glTexSubImage2D.

[erikchen, 2016/01/29 20:32:25]

I added two more parameters: GrPixelConfig and a const void* srcData.

+     */
+    virtual bool allocateTextureStorage(GrBackendObject texture, unsigned width,
+                                        unsigned height) = 0;
+    /*
+     * Deallocate the storage for the given texture.
+     *
+     * Skia does not always destroy its outstanding textures. See
+     * GrContext::abandonContext() for more details. The consumer of Skia is
+     * responsible for making sure that all textures are destroyed, even if this
+     * callback is not invoked.
+     */
+    virtual void deallocateTextureStorage(GrBackendObject texture) = 0;
+
+protected:
+    virtual ~GrTextureStorageAllocator() {}
+};
+
 /**
  * Some textures will be stored such that the upper and left edges of the content meet at the
  * the origin (in texture coord space) and for other textures the lower and left edges meet at
@@ -432,7 +471,8 @@ struct GrSurfaceDesc {
     , fWidth(0)
     , fHeight(0)
     , fConfig(kUnknown_GrPixelConfig)
-    , fSampleCnt(0) {
+    , fSampleCnt(0)
+    , fTextureStorageAllocator(nullptr) {
     }
 
     GrSurfaceFlags         fFlags;  //!< bitfield of TextureFlags
@@ -454,6 +494,13 @@ struct GrSurfaceDesc {
      * max supported count.
      */
     int                    fSampleCnt;
+
+    /**
+     * A custom platform-specific allocator to use in place of TexImage2D. All
+     * surfaces derived from the original surface will have the same value for
+     * fTextureStorageAllocator.
+     */
+    GrTextureStorageAllocator* fTextureStorageAllocator;
 };
 
 // Legacy alias
@@ -469,9 +516,6 @@ enum GrClipType {
 
 ///////////////////////////////////////////////////////////////////////////////
 
-// opaque type for 3D API object handles
-typedef intptr_t GrBackendObject;
-
 
 /** Ownership rules for external GPU resources imported into Skia. */
 enum GrWrapOwnership {