Implement GLHelperReadbackSupport for GLHelper usage.

content/common/gpu/client/gl_helper.h

Index: content/common/gpu/client/gl_helper.h
diff --git a/content/common/gpu/client/gl_helper.h b/content/common/gpu/client/gl_helper.h
index 46db753207217ae13659920803008f68b739df8c..b885dbfd3c22d657e8b3762c95cecde6aab3a2fe 100644
--- a/content/common/gpu/client/gl_helper.h
+++ b/content/common/gpu/client/gl_helper.h
@@ -169,6 +169,12 @@ class CONTENT_EXPORT GLHelper {
     SCALER_QUALITY_BEST = 3,
   };
 
+  enum FormatSupport {
+    FORMAT_NOT_SUPPORTED = 0,
+    FORMAT_SUPPORTED,
+    FORMAT_SUPPORT_UNKNOWN,
+  };
+
   // Copies the block of pixels specified with |src_subrect| from |src_texture|,
   // scales it to |dst_size|, and writes it into |out|.
   // |src_size| is the size of |src_texture|. The result is of format GL_BGRA
@@ -277,8 +283,12 @@ class CONTENT_EXPORT GLHelper {
   // size of the framebuffer.
   void CopyTextureFullImage(GLuint texture, const gfx::Size& size);
 
-  // Check whether rgb565 readback is supported or not.
-  bool CanUseRgb565Readback();
+  // Checks whether the readback (Color read format and type) is supported
+  // for the requested texture format  by the hardware or not.
+  // For ex: some hardwares have rgb565 readback
+  // support when binded with the frame buffer for others it may fail.
+
+  bool IsReadbackConfigSupported(SkBitmap::Config bitmap_format);
 
   // A scaler will cache all intermediate textures and programs
   // needed to scale from a specified size to a destination size.
@@ -328,6 +338,18 @@ class CONTENT_EXPORT GLHelper {
   // 0 if GL_EXT_draw_buffers is not available.
   GLint MaxDrawBuffers();
 
+ private:
+  // IsReadbackConfigSupported does texture bind and attach operations,
+  // better do it in the constructor, and never do it again.
+  // This populates the readback support list at a time once.
+  void InitializeReadbackSupport();
+  void CheckForReadbackSupport(SkBitmap::Config bitmap_format);
+
+  // Helper functions for checking the supported texture formats.
+  // Avoid using this API in between texture operations, as this does some
+  // teture opertions (bind, attach) internally.
+  bool SupportsFormat(GLint format, GLint type);
+
  protected:
   class CopyTextureToImpl;
 
@@ -340,8 +362,7 @@ class CONTENT_EXPORT GLHelper {
   gpu::ContextSupport* context_support_;
   scoped_ptr<CopyTextureToImpl> copy_texture_to_impl_;
   scoped_ptr<GLHelperScaling> scaler_impl_;
-  bool initialized_565_format_check_;
-  bool support_565_format_;
+  FormatSupport format_support_table_[SkBitmap::kConfigCount];
 
   DISALLOW_COPY_AND_ASSIGN(GLHelper);
 };