Reduce jank from favicon downscaling.

components/favicon_base/favicon_util.cc

Index: components/favicon_base/favicon_util.cc
diff --git a/components/favicon_base/favicon_util.cc b/components/favicon_base/favicon_util.cc
index e17ebdf97a875cd2ba0ed535a82d3f6c9a6ba5e6..fbd44eec2a733b09ac329f7ab2d3f0e853aefccc 100644
--- a/components/favicon_base/favicon_util.cc
+++ b/components/favicon_base/favicon_util.cc
@@ -9,6 +9,7 @@
 #include <algorithm>
 #include <cmath>
 
+#include "base/trace_event/trace_event.h"
 #include "build/build_config.h"
 #include "components/favicon_base/favicon_types.h"
 #include "components/favicon_base/select_favicon_frames.h"
@@ -36,6 +37,8 @@ std::vector<gfx::ImagePNGRep> SelectFaviconFramesFromPNGsWithoutResizing(
     const std::vector<favicon_base::FaviconRawBitmapResult>& png_data,
     const std::vector<float>& favicon_scales,
     int favicon_size) {
+  TRACE_EVENT0("browser",
+               "FaviconUtil::SelectFaviconFramesFromPNGsWithoutResizing");
   std::vector<gfx::ImagePNGRep> png_reps;
   if (png_data.empty())
     return png_reps;
@@ -166,6 +169,8 @@ gfx::Image SelectFaviconFramesFromPNGs(
     const std::vector<favicon_base::FaviconRawBitmapResult>& png_data,
     const std::vector<float>& favicon_scales,
     int favicon_size) {
+  TRACE_EVENT0("browser", "FaviconUtil::SelectFaviconFramesFromPNGs");
+
   // Create image reps for as many scales as possible without resizing
   // the bitmap data or decoding it. FaviconHandler stores already resized
   // favicons into history so no additional resizing should be needed in the
@@ -245,4 +250,49 @@ gfx::Image SelectFaviconFramesFromPNGs(
   return gfx::Image(png_reps);
 }
 
+favicon_base::FaviconRawBitmapResult ResizeFaviconResultSlow(
+    const std::vector<favicon_base::FaviconRawBitmapResult>&
+        favicon_bitmap_results,
+    int desired_size_in_pixel) {
+  TRACE_EVENT0("browser", "FaviconUtil::ResizeFaviconResultSlow");
+
+  if (favicon_bitmap_results.empty() || !favicon_bitmap_results[0].is_valid())
+    return favicon_base::FaviconRawBitmapResult();
+
+  favicon_base::FaviconRawBitmapResult bitmap_result =
+      favicon_bitmap_results[0];
+
+  // If the desired size is 0, SelectFaviconFrames() will return the largest
+  // bitmap without doing any resizing. As |favicon_bitmap_results| has bitmap
+  // data for a single bitmap, return it and avoid an unnecessary decode.
+  if (desired_size_in_pixel == 0)
+    return bitmap_result;
+
+  // If history bitmap is already desired pixel size, return early.
+  if (bitmap_result.pixel_size.width() == desired_size_in_pixel &&
+      bitmap_result.pixel_size.height() == desired_size_in_pixel)
+    return bitmap_result;
+
+  // Convert raw bytes to SkBitmap, resize via SelectFaviconFrames(), then
+  // convert back.
+  std::vector<float> desired_favicon_scales;
+  desired_favicon_scales.push_back(1.0f);
+
+  gfx::Image resized_image = favicon_base::SelectFaviconFramesFromPNGs(
+      favicon_bitmap_results, desired_favicon_scales, desired_size_in_pixel);
+
+  std::vector<unsigned char> resized_bitmap_data;
+  if (!gfx::PNGCodec::EncodeBGRASkBitmap(resized_image.AsBitmap(), false,

[aelias_OOO_until_Jul13, 2016/09/06 20:46:42]

OK, if the "Fast" here is the main point of debate, I removed it from PS#2 since
I only measured a ~20% CPU saving from that, and the main benefit of the patch
is the threading change.

I want to explain my underlying assumptions a bit though:
1. Android is more demanding on both CPU and RAM than desktop, so if the
tradeoff works for us it's probably the right one everywhere.
2. Doing all this decompression/recompression of PNGs seems like a bad practice
since the CPU cost is extravagant.  The image needs to be fully uncompressed for
display anyway so it's not obvious what is really achieved by the recompression
here.  I'm pretty sure there exist some deeper favicon caching policy
improvements we could be doing that would be more efficient overall, but for now
the threading fix is still a cherry-pickable strict improvement.

+                                         &resized_bitmap_data)) {
+    return favicon_base::FaviconRawBitmapResult();
+  }
+
+  bitmap_result.bitmap_data = base::RefCountedBytes::TakeVector(
+      &resized_bitmap_data);
+  bitmap_result.pixel_size =
+      gfx::Size(desired_size_in_pixel, desired_size_in_pixel);
+
+  return bitmap_result;
+}
+
 }  // namespace favicon_base