Complete disable_gl_rgb_format workaround for Mali-400 GPU

gpu/command_buffer/service/gles2_cmd_decoder.cc

Index: gpu/command_buffer/service/gles2_cmd_decoder.cc
diff --git a/gpu/command_buffer/service/gles2_cmd_decoder.cc b/gpu/command_buffer/service/gles2_cmd_decoder.cc
index ae331e5a4a080d4cf275e8cb35d2caf30011a28a..55f34c3481fca1468cdd96638d4a5f1901d6fea1 100644
--- a/gpu/command_buffer/service/gles2_cmd_decoder.cc
+++ b/gpu/command_buffer/service/gles2_cmd_decoder.cc
@@ -1851,6 +1851,8 @@ class GLES2DecoderImpl : public GLES2Decoder, public ErrorStateClient {
   }
 
   bool BackBufferHasAlpha() const {
+    if (state_.emulating_rgb_with_rgba)
+      return false;
     if (back_buffer_draw_buffer_ == GL_NONE)
       return false;
     if (offscreen_target_frame_buffer_.get()) {
@@ -2753,9 +2755,12 @@ bool GLES2DecoderImpl::Initialize(const scoped_refptr<gfx::GLSurface>& surface,
       } else {
         offscreen_target_samples_ = 1;
         offscreen_target_color_format_ =
-            attrib_parser.alpha_size > 0 || workarounds().disable_gl_rgb_format
-                ? GL_RGBA
-                : GL_RGB;
+            (attrib_parser.alpha_size > 0) ? GL_RGBA : GL_RGB;
+        if (offscreen_target_color_format_ == GL_RGB &&
+            workarounds().disable_gl_rgb_format) {
+          offscreen_target_color_format_ = GL_RGBA;
+          state_.emulating_rgb_with_rgba = true;
+        }
       }
 
       // ANGLE only supports packed depth/stencil formats, so use it if it is
@@ -2778,9 +2783,12 @@ bool GLES2DecoderImpl::Initialize(const scoped_refptr<gfx::GLSurface>& surface,
       }
     } else {
       offscreen_target_color_format_ =
-          attrib_parser.alpha_size > 0 || workarounds().disable_gl_rgb_format
-              ? GL_RGBA
-              : GL_RGB;
+          (attrib_parser.alpha_size > 0) ? GL_RGBA : GL_RGB;
+      if (offscreen_target_color_format_ == GL_RGB &&
+          workarounds().disable_gl_rgb_format) {
+        offscreen_target_color_format_ = GL_RGBA;
+        state_.emulating_rgb_with_rgba = true;
+      }
 
       // If depth is requested at all, use the packed depth stencil format if
       // it's available, as some desktop GL drivers don't support any non-packed
@@ -6145,7 +6153,15 @@ void GLES2DecoderImpl::ClearUnclearedAttachments(
     // We should always use alpha == 0 here, because 1) some draw buffers may
     // have alpha and some may not; 2) we won't have the same situation as the
     // back buffer where alpha channel exists but is not requested.
-    glClearColor(0.0f, 0.0f, 0.0f, 0.0f);
+    float clear_alpha = 0.0f;
+    if (workarounds().disable_gl_rgb_format &&
+        (GLES2Util::GetChannelsForFormat(
+             framebuffer->GetColorAttachment0Format()) &
+         0x0008) == 0) {
+      clear_alpha = 1.0f;
+    }
+    glClearColor(0.0f, 0.0f, 0.0f, clear_alpha);
+
     state_.SetDeviceColorMask(GL_TRUE, GL_TRUE, GL_TRUE, GL_TRUE);
     clear_bits |= GL_COLOR_BUFFER_BIT;
     if (feature_info_->feature_flags().ext_draw_buffers ||