Moved the majority of WebGL functionality into WebGLRenderingContextBase

Source/core/html/canvas/WebGLDepthTexture.cpp

Index: Source/core/html/canvas/WebGLDepthTexture.cpp
diff --git a/Source/core/html/canvas/WebGLDepthTexture.cpp b/Source/core/html/canvas/WebGLDepthTexture.cpp
index 6a450c2eb426d7edf548cc0d519fa92aa4f8289e..032eff4181d7cdb21783598c1b667d19508e2ec1 100644
--- a/Source/core/html/canvas/WebGLDepthTexture.cpp
+++ b/Source/core/html/canvas/WebGLDepthTexture.cpp
@@ -31,7 +31,7 @@
 
 namespace WebCore {
 
-WebGLDepthTexture::WebGLDepthTexture(WebGLRenderingContext* context)
+WebGLDepthTexture::WebGLDepthTexture(WebGLRenderingContextBase* context)
     : WebGLExtension(context)
 {
     ScriptWrappable::init(this);
@@ -47,12 +47,12 @@ WebGLExtension::ExtensionName WebGLDepthTexture::getName() const
     return WebGLDepthTextureName;
 }
 
-PassRefPtr<WebGLDepthTexture> WebGLDepthTexture::create(WebGLRenderingContext* context)
+PassRefPtr<WebGLDepthTexture> WebGLDepthTexture::create(WebGLRenderingContextBase* context)
 {
     return adoptRef(new WebGLDepthTexture(context));
 }
 
-bool WebGLDepthTexture::supported(WebGLRenderingContext* context)
+bool WebGLDepthTexture::supported(WebGLRenderingContextBase* context)
 {
     Extensions3D* extensions = context->graphicsContext3D()->getExtensions();
     // Emulating the UNSIGNED_INT_24_8_WEBGL texture internal format in terms