2222.patch

From: csagan5 <32685696+csagan5@users.noreply.github.com>
Date: Sat, 24 Mar 2018 05:18:03 +0100
Subject: Canvas: fingerprinting mitigations for image data, font metrics and
 webGL

Disable webGL renderering info, add shuffling to TextMetrics;
additionally, the color data returned by ToBlob and ToDataURL will
contain randomly manipulated pixels (maximum 10) that slightly
change the color R,G,B components without visibly altering the rendering.

Credits to Slaviro (https://github.com/Slaviro) for coming up with a better
approach to change color components.
---
 .../renderer/core/html/canvas/text_metrics.cc      |  20 +++
 .../blink/renderer/core/html/canvas/text_metrics.h |   2 +
 .../canvas/canvas2d/base_rendering_context_2d.cc   |   3 +
 .../canvas/canvas2d/canvas_rendering_context_2d.cc |   6 +-
 .../modules/webgl/webgl_debug_renderer_info.cc     |   4 +-
 .../platform/graphics/image_data_buffer.cc         | 137 +++++++++++++++++++++
 .../renderer/platform/graphics/image_data_buffer.h |   2 +
 7 files changed, 171 insertions(+), 3 deletions(-)

diff --git a/third_party/blink/renderer/core/html/canvas/text_metrics.cc b/third_party/blink/renderer/core/html/canvas/text_metrics.cc
--- a/third_party/blink/renderer/core/html/canvas/text_metrics.cc
+++ b/third_party/blink/renderer/core/html/canvas/text_metrics.cc
@@ -49,6 +49,25 @@
   return 0;
 }
 
+void TextMetrics::Shuffle(const double amt) {
+  double adjusted = 1 + amt;
+
+  // x-direction
+  width_ *= adjusted;
+  actual_bounding_box_left_ *= adjusted;
+  actual_bounding_box_right_ *= adjusted;
+
+  // y-direction
+  font_bounding_box_ascent_ *= adjusted;
+  font_bounding_box_descent_ *= adjusted;
+  actual_bounding_box_ascent_ *= adjusted;
+  actual_bounding_box_descent_ *= adjusted;
+  em_height_ascent_ *= adjusted;
+  em_height_descent_ *= adjusted;
+  baselines_ *= adjusted;
+}
+
+
 void TextMetrics::Update(const Font& font,
                          const TextDirection& direction,
                          const TextBaseline& baseline,