Fix base level for generateMipmap in blink

Source/modules/webgl/WebGLRenderingContextBase.cpp

Index: Source/modules/webgl/WebGLRenderingContextBase.cpp
diff --git a/Source/modules/webgl/WebGLRenderingContextBase.cpp b/Source/modules/webgl/WebGLRenderingContextBase.cpp
index 3b92a338ac5b7929863a1d99407ce9f06219c2a2..48001f89c3b5bfda4e72e243c9441403580081ea 100644
--- a/Source/modules/webgl/WebGLRenderingContextBase.cpp
+++ b/Source/modules/webgl/WebGLRenderingContextBase.cpp
@@ -2381,7 +2381,7 @@ void WebGLRenderingContextBase::generateMipmap(GLenum target)
     if (!tex)
         return;
     if (!tex->canGenerateMipmaps()) {
-        synthesizeGLError(GL_INVALID_OPERATION, "generateMipmap", "level 0 not power of 2 or not all the same size");
+        synthesizeGLError(GL_INVALID_OPERATION, "generateMipmap", "cannot generate mipmaps");
         return;
     }
     if (tex->getInternalFormat(target, 0) == GL_SRGB_EXT || tex->getInternalFormat(target, 0) == GL_SRGB_ALPHA_EXT) {