Revert of webgl: use immutable texture for the default FBO.

third_party/WebKit/Source/platform/graphics/gpu/DrawingBuffer.cpp

Index: third_party/WebKit/Source/platform/graphics/gpu/DrawingBuffer.cpp
diff --git a/third_party/WebKit/Source/platform/graphics/gpu/DrawingBuffer.cpp b/third_party/WebKit/Source/platform/graphics/gpu/DrawingBuffer.cpp
index 3a62898318e34cae2523f1aaafa0e343ab0c2a05..c8b928e6ba2d410cba0eae8b5697184f5e3e19a7 100644
--- a/third_party/WebKit/Source/platform/graphics/gpu/DrawingBuffer.cpp
+++ b/third_party/WebKit/Source/platform/graphics/gpu/DrawingBuffer.cpp
@@ -151,7 +151,6 @@
     , m_multisampleExtensionSupported(multisampleExtensionSupported)
     , m_packedDepthStencilExtensionSupported(packedDepthStencilExtensionSupported)
     , m_discardFramebufferSupported(discardFramebufferSupported)
-    , m_storageTextureSupported(false)
     , m_fbo(0)
     , m_depthStencilBuffer(0)
     , m_depthBuffer(0)
@@ -306,8 +305,7 @@
             m_context->discardFramebufferEXT(GL_FRAMEBUFFER, 3, attachments);
         }
     } else {
-        m_context->copySubTextureCHROMIUM(GL_TEXTURE_2D, m_colorBuffer.textureId, frontColorBufferMailbox->textureInfo.textureId,
-            0, 0, 0, 0, m_size.width(), m_size.height(), GL_FALSE, GL_FALSE, GL_FALSE);
+        m_context->copyTextureCHROMIUM(GL_TEXTURE_2D, m_colorBuffer.textureId, frontColorBufferMailbox->textureInfo.textureId, GL_RGBA, GL_UNSIGNED_BYTE, GL_FALSE, GL_FALSE, GL_FALSE);
     }
 
     restoreFramebufferBindings();
@@ -451,7 +449,6 @@
         }
     }
     m_sampleCount = std::min(4, maxSampleCount);
-    m_storageTextureSupported = m_extensionsUtil->supportsExtension("GL_EXT_texture_storage");
 
     m_fbo = m_context->createFramebuffer();
 
@@ -962,6 +959,12 @@
     }
 }
 
+void DrawingBuffer::texImage2DResourceSafe(GLenum target, GLint level, GLenum internalformat, GLsizei width, GLsizei height, GLint border, GLenum format, GLenum type, GLint unpackAlignment)
+{
+    ASSERT(unpackAlignment == 1 || unpackAlignment == 2 || unpackAlignment == 4 || unpackAlignment == 8);
+    m_context->texImage2D(target, level, internalformat, width, height, border, format, type, 0);
+}
+
 void DrawingBuffer::allocateTextureMemory(TextureInfo* info, const IntSize& size)
 {
     if (RuntimeEnabledFeatures::webGLImageChromiumEnabled()) {
@@ -974,18 +977,7 @@
         }
     }
 
-    if (m_storageTextureSupported) {
-        if (info->immutable) {
-            m_context->deleteTexture(info->textureId);
-            info->textureId = createColorTexture();
-        }
-
-        // TODO(dshwang): GL_BGRA8_EXT can be better in some platforms. crbug.com/557848
-        m_context->texStorage2DEXT(GL_TEXTURE_2D, 1, m_internalRenderbufferFormat, size.width(), size.height());
-        info->immutable = true;
-        return;
-    }
-    m_context->texImage2D(GL_TEXTURE_2D, 0, m_internalColorFormat, size.width(), size.height(), 0, m_colorFormat, GL_UNSIGNED_BYTE, 0);
+    texImage2DResourceSafe(GL_TEXTURE_2D, 0, m_internalColorFormat, size.width(), size.height(), 0, m_colorFormat, GL_UNSIGNED_BYTE);
 }
 
 void DrawingBuffer::deleteChromiumImageForTexture(TextureInfo* info)