Record UMA stats for Blink decoded image types

Source/platform/image-decoders/ImageDecoder.h

Index: Source/platform/image-decoders/ImageDecoder.h
diff --git a/Source/platform/image-decoders/ImageDecoder.h b/Source/platform/image-decoders/ImageDecoder.h
index 83c0cb9b0380e2e5e95850be4014a720a054b030..7224eecb02f30d222b8f1cb2508c5f5327b67d7e 100644
--- a/Source/platform/image-decoders/ImageDecoder.h
+++ b/Source/platform/image-decoders/ImageDecoder.h
@@ -49,6 +49,23 @@ typedef Vector<char> ColorProfile;
 
 namespace blink {
 
+enum DecodedImageType {
+    // These values are histogrammed over time; do not change their ordinal
+    // values.  When deleting an image type, replace it with a dummy value;
+    // when adding an image type, do so at the bottom (and update DecodedImageTypeMax).
+    // Also, this enum should be in sync with the 'DecodedImageType' enum in
+    // tools/metrics/histograms/histograms.xml
+    ImageUnknown = 0,
+    ImageJPEG,
+    ImagePNG,
+    ImageGIF,
+    ImageWebP,
+    ImageICO,
+    ImageBMP,
+
+    DecodedImageTypeMax = ImageBMP // Must equal the last "real" image type above.
+};
+
 // ImagePlanes can be used to decode color components into provided buffers instead of using an ImageFrame.
 class PLATFORM_EXPORT ImagePlanes {
 public:
@@ -326,6 +343,14 @@ protected:
     // Decodes the requested frame.
     virtual void decode(size_t) = 0;
 
+    // Report image stats if it's NOT a trivial 1x1 image.
+    void reportStats(DecodedImageType type) const
+    {
+        if (isDecodedSizeAvailable() && (size().width() > 1 || size().height() > 1)) {
+            Platform::current()->histogramEnumeration("Blink.DecodedImageType", type, DecodedImageTypeMax + 1);
+        }
+    }
+
     RefPtr<SharedBuffer> m_data; // The encoded data.
     Vector<ImageFrame, 1> m_frameBufferCache;
     bool m_premultiplyAlpha;