WebGL: clarify which Front or Back buffer is used by each API.

Source/core/html/canvas/WebGLRenderingContextBase.cpp

Index: Source/core/html/canvas/WebGLRenderingContextBase.cpp
diff --git a/Source/core/html/canvas/WebGLRenderingContextBase.cpp b/Source/core/html/canvas/WebGLRenderingContextBase.cpp
index 151e37c8648804dee30863e729eda0cf64fff09c..2a4ccbe7acc1214b12f041e069793599009585e1 100644
--- a/Source/core/html/canvas/WebGLRenderingContextBase.cpp
+++ b/Source/core/html/canvas/WebGLRenderingContextBase.cpp
@@ -915,26 +915,6 @@ void WebGLRenderingContextBase::paintRenderingResultsToCanvas(SourceBuffer sourc
         drawingBuffer()->bind();
 }
 
-PassRefPtrWillBeRawPtr<ImageData> WebGLRenderingContextBase::paintRenderingResultsToImageData()
-{
-    if (isContextLost())
-        return nullptr;
-
-    clearIfComposited();
-    drawingBuffer()->commit();
-    int width, height;
-    RefPtr<Uint8ClampedArray> imageDataPixels = drawingBuffer()->paintRenderingResultsToImageData(width, height);
-    if (!imageDataPixels)
-        return nullptr;
-
-    if (m_framebufferBinding)
-        webContext()->bindFramebuffer(GL_FRAMEBUFFER, objectOrZero(m_framebufferBinding.get()));
-    else
-        drawingBuffer()->bind();
-
-    return ImageData::create(IntSize(width, height), imageDataPixels);
-}
-
 void WebGLRenderingContextBase::reshape(int width, int height)
 {
     if (isContextLost())
@@ -3557,11 +3537,7 @@ void WebGLRenderingContextBase::texImage2D(GLenum target, GLint level, GLenum in
         }
     }
 
-    RefPtrWillBeRawPtr<ImageData> imageData = canvas->getImageData();
-    if (imageData)
-        texImage2D(target, level, internalformat, format, type, imageData.get(), exceptionState);
-    else
-        texImage2DImpl(target, level, internalformat, format, type, canvas->copiedImage(), WebGLImageConversion::HtmlDomCanvas, m_unpackFlipY, m_unpackPremultiplyAlpha, exceptionState);
+    texImage2DImpl(target, level, internalformat, format, type, canvas->copiedImage(HTMLCanvasElement::Back), WebGLImageConversion::HtmlDomCanvas, m_unpackFlipY, m_unpackPremultiplyAlpha, exceptionState);
 }
 
 PassRefPtr<Image> WebGLRenderingContextBase::videoFrameToImage(HTMLVideoElement* video, BackingStoreCopy backingStoreCopy)
@@ -3795,11 +3771,7 @@ void WebGLRenderingContextBase::texSubImage2D(GLenum target, GLint level, GLint
         || !validateTexFunc("texSubImage2D", TexSubImage2D, SourceHTMLCanvasElement, target, level, format, canvas->width(), canvas->height(), 0, format, type, xoffset, yoffset))
         return;
 
-    RefPtrWillBeRawPtr<ImageData> imageData = canvas->getImageData();
-    if (imageData)
-        texSubImage2D(target, level, xoffset, yoffset, format, type, imageData.get(), exceptionState);
-    else
-        texSubImage2DImpl(target, level, xoffset, yoffset, format, type, canvas->copiedImage(), WebGLImageConversion::HtmlDomCanvas, m_unpackFlipY, m_unpackPremultiplyAlpha, exceptionState);
+    texSubImage2DImpl(target, level, xoffset, yoffset, format, type, canvas->copiedImage(HTMLCanvasElement::Back), WebGLImageConversion::HtmlDomCanvas, m_unpackFlipY, m_unpackPremultiplyAlpha, exceptionState);
 }
 
 void WebGLRenderingContextBase::texSubImage2D(GLenum target, GLint level, GLint xoffset, GLint yoffset,