Clamp YUV videos to their visible size in the shader

cc/output/gl_renderer.cc

Index: cc/output/gl_renderer.cc
diff --git a/cc/output/gl_renderer.cc b/cc/output/gl_renderer.cc
index f2029f3a50d60dd1db9d4e65015c310ebe783a28..f53ab0db06205e1fe13c8ccebca0f16681169cbc 100644
--- a/cc/output/gl_renderer.cc
+++ b/cc/output/gl_renderer.cc
@@ -1832,6 +1832,7 @@ void GLRenderer::DrawYUVVideoQuad(const DrawingFrame* frame,
   int matrix_location = -1;
   int tex_scale_location = -1;
   int tex_offset_location = -1;
+  int clamp_rect_location = -1;
   int y_texture_location = -1;
   int u_texture_location = -1;
   int v_texture_location = -1;
@@ -1852,6 +1853,7 @@ void GLRenderer::DrawYUVVideoQuad(const DrawingFrame* frame,
     a_texture_location = program->fragment_shader().a_texture_location();
     yuv_matrix_location = program->fragment_shader().yuv_matrix_location();
     yuv_adj_location = program->fragment_shader().yuv_adj_location();
+    clamp_rect_location = program->fragment_shader().clamp_rect_location();
     alpha_location = program->fragment_shader().alpha_location();
   } else {
     const VideoYUVProgram* program = GetVideoYUVProgram(tex_coord_precision);
@@ -1865,6 +1867,7 @@ void GLRenderer::DrawYUVVideoQuad(const DrawingFrame* frame,
     v_texture_location = program->fragment_shader().v_texture_location();
     yuv_matrix_location = program->fragment_shader().yuv_matrix_location();
     yuv_adj_location = program->fragment_shader().yuv_adj_location();
+    clamp_rect_location = program->fragment_shader().clamp_rect_location();
     alpha_location = program->fragment_shader().alpha_location();
   }
 
@@ -1876,6 +1879,14 @@ void GLRenderer::DrawYUVVideoQuad(const DrawingFrame* frame,
       gl_->Uniform2f(tex_offset_location,
                      quad->tex_coord_rect.x(),
                      quad->tex_coord_rect.y()));
+  // Clamping to half a texel inside the tex coord rect prevents bilinear
+  // filtering from filtering outside the tex coord rect.
+  gfx::RectF clamp_rect(quad->tex_coord_rect);
+  clamp_rect.Inset(0.5f / quad->tex_size.width(),
+                   0.5f / quad->tex_size.height());
+  GLC(gl_, gl_->Uniform4f(clamp_rect_location, clamp_rect.x(), clamp_rect.y(),
+                          clamp_rect.right(), clamp_rect.bottom()));
+
   GLC(gl_, gl_->Uniform1i(y_texture_location, 1));
   GLC(gl_, gl_->Uniform1i(u_texture_location, 2));
   GLC(gl_, gl_->Uniform1i(v_texture_location, 3));