Fix handling of broken GIFs with weird frame sizes

Source/platform/image-decoders/gif/GIFImageReader.cpp

Index: Source/platform/image-decoders/gif/GIFImageReader.cpp
diff --git a/Source/platform/image-decoders/gif/GIFImageReader.cpp b/Source/platform/image-decoders/gif/GIFImageReader.cpp
index 42db80edb56dab57fb92fcea2f215a966c84b03b..4f4af81b8e547d15a55e4673706f16b58dc38367 100644
--- a/Source/platform/image-decoders/gif/GIFImageReader.cpp
+++ b/Source/platform/image-decoders/gif/GIFImageReader.cpp
@@ -437,14 +437,10 @@ bool GIFImageReader::parseData(size_t dataPosition, size_t len, GIFImageDecoder:
             // This is the height and width of the "screen" or frame into which images are rendered. The
             // individual images can be smaller than the screen size and located with an origin anywhere
             // within the screen.
+            // Note that we don't inform the client of the size yet, as it might change after we read the first frame's image header.

[Peter Kasting, 2015/01/13 01:47:33]

Nit: I still think all the comments in this change ought to be wrapped at 80
columns for readability.

             m_screenWidth = GETINT16(currentComponent);
             m_screenHeight = GETINT16(currentComponent + 2);
 
-            // CALLBACK: Inform the decoderplugin of our size.
-            // Note: A subsequent frame might have dimensions larger than the "screen" dimensions.
-            if (m_client && !m_client->setSize(m_screenWidth, m_screenHeight))
-                return false;
-
             const size_t globalColorMapColors = 2 << (currentComponent[4] & 0x07);
 
             if ((currentComponent[4] & 0x80) && globalColorMapColors > 0) { /* global map */
@@ -632,29 +628,23 @@ bool GIFImageReader::parseData(size_t dataPosition, size_t len, GIFImageDecoder:
             width  = GETINT16(currentComponent + 4);
             height = GETINT16(currentComponent + 6);
 
-            /* Work around broken GIF files where the logical screen
-             * size has weird width or height.  We assume that GIF87a
-             * files don't contain animations.
-             */
-            if (currentFrameIsFirstFrame()
-                && ((m_screenHeight < height) || (m_screenWidth < width) || (m_version == 87))) {
-                m_screenHeight = height;
-                m_screenWidth = width;
-                xOffset = 0;
-                yOffset = 0;
-
-                // CALLBACK: Inform the decoderplugin of our size.
-                if (m_client && !m_client->setSize(m_screenWidth, m_screenHeight))
-                    return false;
+            // Some GIF files have frames that don't fit in the specified overall image size.
+            // For the first frame, we can simply enlarge the image size to allow the frame to
+            // be visible.  We can't do this on subsequent frames because the rest of the
+            // decoding infrastructure assumes the image size won't change as we continue
+            // decoding, so any subsequent frames that are even larger will be cropped.
+            // Luckily, handling just the first frame is sufficient to deal with most cases,
+            // e.g. ones where the image size is erroneously set to zero, since usually the
+            // first frame completely fills the image.
+            if (currentFrameIsFirstFrame()) {
+                m_screenHeight = std::max(m_screenHeight, yOffset + height);
+                m_screenWidth = std::max(m_screenWidth, xOffset + width);
             }
 
-            // Work around more broken GIF files that have zero image width or height
-            if (!height || !width) {
-                height = m_screenHeight;
-                width = m_screenWidth;
-                if (!height || !width)
-                    return false;
-            }
+            // Inform the client of the final size.
+            if (!m_sentSizeToClient && m_client && !m_client->setSize(m_screenWidth, m_screenHeight))
+                return false;
+            m_sentSizeToClient = true;
 
             if (query == GIFImageDecoder::GIFSizeQuery) {
                 // The decoder needs to stop. Hand back the number of bytes we consumed from
@@ -668,9 +658,15 @@ bool GIFImageReader::parseData(size_t dataPosition, size_t len, GIFImageDecoder:
             GIFFrameContext* currentFrame = m_frames.last().get();
 
             currentFrame->setHeaderDefined();
+
+            // Work around more broken GIF files that have zero image width or height.
+            if (!height || !width) {
+                height = m_screenHeight;
+                width = m_screenWidth;
+                if (!height || !width)
+                    return false;
+            }
             currentFrame->setRect(xOffset, yOffset, width, height);
-            m_screenWidth = std::max(m_screenWidth, width);
-            m_screenHeight = std::max(m_screenHeight, height);
             currentFrame->setInterlaced(currentComponent[8] & 0x40);
 
             // Overlaying interlaced, transparent GIFs over