cc: Cache highp_threshold in TexCoordPrecisionRequired

cc/output/shader.h

 // Copyright 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CC_OUTPUT_SHADER_H_
 #define CC_OUTPUT_SHADER_H_
 
 #include <string>
 
 #include "base/basictypes.h"
@@ skipping 10 matching lines @@
 }
 
 namespace cc {
 
 enum TexCoordPrecision {
   TexCoordPrecisionNA,
   TexCoordPrecisionMedium,
   TexCoordPrecisionHigh,
 };
 
+// Note: The highp_threshold_cache must be provided by the caller to make
+// the caching multi-thread/context safe in an easy low-overhead manner.
+// The caller must make sure to clear highp_threshold_cache to 0, so it can be
+// reinitialized, if a new or different context is used.
 CC_EXPORT TexCoordPrecision TexCoordPrecisionRequired(
     WebKit::WebGraphicsContext3D* context,
+    int *highp_threshold_cache,
     int highp_threshold_min,
     gfx::Point max_coordinate);
 
 CC_EXPORT TexCoordPrecision TexCoordPrecisionRequired(
     WebKit::WebGraphicsContext3D* context,
+    int *highp_threshold_cache,
     int highp_threshold_min,
     gfx::Size max_size);
 
 class VertexShaderPosTex {
  public:
   VertexShaderPosTex();
 
   void Init(WebKit::WebGraphicsContext3D* context,
             unsigned program,
             bool using_bind_uniform,
@@ skipping 557 matching lines @@
   int tex_transform_location_;
   int frequency_location_;
   int color_location_;
 
   DISALLOW_COPY_AND_ASSIGN(FragmentShaderCheckerboard);
 };
 
 }  // namespace cc
 
 #endif  // CC_OUTPUT_SHADER_H_