gpu: Allow CopyTexImage to be called with StreamTextures and GLImageSync.

BUG=374962
R=sievers@chromium.org

Review URL: https://codereview.chromium.org/549253003

Cr-Commit-Position: refs/heads/master@{#293855}

content/common/gpu/stream_texture_android.cc

@@ -203,7 +203,6 @@ void StreamTexture::ReleaseTexImage(unsigned target) {
 }
 
 bool StreamTexture::CopyTexImage(unsigned target) {
-  NOTREACHED();
   return false;
 }
 

gpu/command_buffer/service/stream_texture_manager_in_process_android.cc

@@ -74,7 +74,6 @@ void GLImageImpl::ReleaseTexImage(unsigned target) {
 }
 
 bool GLImageImpl::CopyTexImage(unsigned target) {
-  NOTREACHED();
   return false;
 }
 

gpu/command_buffer/service/texture_definition.cc

@@ -85,7 +85,6 @@ void GLImageSync::ReleaseTexImage(unsigned target) {
 }
 
 bool GLImageSync::CopyTexImage(unsigned target) {
-  NOTREACHED();
   return false;
 }