Batch-fix clang-tidy warnings around the Canvas code base.

 - Nested namespaces can be concatenated
   (modernize-concat-nested-namespaces)
 - Use range-based for loop instead
   (modernize-loop-convert
 - Use '= default' to define a trivial destructor
   (modernize-use-equals-default)
 - Use '= default' to define a trivial copy constructor
   (modernize-use-equals-default)
 - Initializer for member 'sampling' is redundant
   (readability-redundant-member-init)
 - Member initializer for 'needs_begin_frame_' is redundant
   (modernize-use-default-member-init
 - Use default member initializer for 'save_count_'
   (modernize-use-default-member-init)
 - Argument name 'coded_size' in comment does not match parameter name
   'size' (bugprone-argument-comment)

Change-Id: I2c83e09c2fcea690dbc3aa3efdfac177d1607930
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3871599


Reviewed-by: Justin Novosad <junov@chromium.org>
Reviewed-by: Vasiliy Telezhnikov <vasilyt@chromium.org>
Commit-Queue: Jean-Philippe Gravel <jpgravel@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1044788}